9 The topology file is built following the |Gromacs| specification for a
10 molecular topology. A :ref:`top` file can be generated by
11 :ref:`pdb2gmx <gmx pdb2gmx>`. All possible entries in the topology file are
12 listed in :numref:`Tables %s <tab-topfile1>` and
13 :numref:`%s <tab-topfile2>`. Also tabulated are: all the units of
14 the parameters, which interactions can be perturbed for free energy
15 calculations, which bonded interactions are used by
16 :ref:`grompp <gmx grompp>` for generating exclusions, and which bonded
17 interactions can be converted to constraints by :ref:`grompp <gmx grompp>`.
19 .. |VCR| replace:: V\ :math:`^{(cr)}`
20 .. |WCR| replace:: W\ :math:`^{(cr)}`
21 .. |CRO| replace:: :math:`^{(cr)}`
22 .. |TREF| replace:: :numref:`Table %s <tab-topfile2>`
23 .. |AKJM| replace:: :math:`a~\mathrm{kJ~mol}^{-1}`
24 .. |KJN6| replace:: :math:`\mathrm{kJ~mol}^{-1}~\mathrm{nm}^{-6}`
25 .. |BNM| replace:: :math:`b~\mathrm{nm}^{-1}`
26 .. |C6LJ| replace:: :math:`c_6`
27 .. |STAR| replace:: :math:`^{(*)}`
28 .. |NREX| replace:: :math:`n_{ex}^{(nrexcl)}`
29 .. |QEMU| replace:: :math:`q` (e); :math:`m` (u)
30 .. |MQM| replace:: :math:`q,m`
34 .. table:: The :ref:`topology <top>` file.
36 +------------------------------------------------------------------------------------------------------------+
38 +===================+===========================+=====+====+=========================================+=======+
39 | interaction type | directive | # | f. | parameters | F. E. |
41 +-------------------+---------------------------+-----+----+-----------------------------------------+-------+
42 | *mandatory* | ``defaults`` | non-bonded function type; |
43 | | | combination rule\ |CRO|; |
44 | | | generate pairs (no/yes); |
45 | | | fudge LJ (); fudge QQ () |
46 +-------------------+---------------------------+------------------------------------------------------------+
47 | *mandatory* | ``atomtypes`` | atom type; m (u); q (e); particle type; |
49 +-------------------+---------------------------+------------------------------------------------------------+
50 | | ``bondtypes`` | (see |TREF|, directive ``bonds``) |
52 | | ``pairtypes`` | (see |TREF|, directive ``pairs``) |
54 | | ``angletypes`` | (see |TREF|, directive ``angles``) |
56 | | ``dihedraltypes``\ |STAR| | (see |TREF|, directive ``dihedrals``) |
58 | | ``constrainttypes`` | (see |TREF|, directive ``constraints``) |
59 +-------------------+---------------------------+-----+----+-------------------------------------------------+
60 | LJ | ``nonbond_params`` | 2 | 1 | |VCR| ; |WCR| |
62 | Buckingham | ``nonbond_params`` | 2 | 2 | |AKJM| ; |BNM|; |
63 | | | | | |C6LJ| (|KJN6|) |
64 +-------------------+---------------------------+-----+----+-------------------------------------------------+
68 +------------------------------------------------------------------------------------------------------------+
69 | Molecule definition(s) |
70 +===================+===========================+============================================================+
71 | *mandatory* | ``moleculetype`` | molecule name; |NREX| |
72 +-------------------+---------------------------+-----+----------------------------------------------+-------+
73 | *mandatory* | ``atoms`` | 1 | atom type; residue number; | type |
74 | | | | residue name; atom name; | |
75 | | | | charge group number; |QEMU| | |MQM| |
76 +-------------------+---------------------------+-----+----------------------------------------------+-------+
77 | intra-molecular interaction and geometry definitions as described in |TREF| |
78 +------------------------------------------------------------------------------------------------------------+
82 +-------------+---------------+------------------------------------+
84 +=============+===============+====================================+
85 | *mandatory* | ``system`` | system name |
86 +-------------+---------------+------------------------------------+
87 | *mandatory* | ``molecules`` | molecule name; number of molecules |
88 +-------------+---------------+------------------------------------+
92 +------------------------------+----------------------------------------------------+
93 | Inter-molecular interactions | |
94 +==============================+====================================================+
95 | *optional* | ``intermolecular_interactions`` |
96 +------------------------------+----------------------------------------------------+
97 | one or more bonded interactions as described in |TREF|, with two or more atoms, |
98 | no interactions that generate exclusions, no constraints, use global atom numbers |
99 +-----------------------------------------------------------------------------------+
103 '\# at' is the required number of atom type indices for this directive
104 'f. tp' is the value used to select this function type
105 'F. E.' indicates which of the parameters can be interpolated in free energy calculations
106 |CRO| the combination rule determines the type of LJ parameters, see
107 |STAR| for ``dihedraltypes`` one can specify 4 atoms or the inner (outer for improper) 2 atoms
108 |NREX| exclude neighbors :math:`n_{ex}` bonds away for non-bonded interactions
109 For free energy calculations, type, :math:`q` and :math:`m` or no parameters should be added
110 for topology 'B' (:math:`\lambda = 1`) on the same line, after the normal parameters.
112 .. |BZERO| replace:: :math:`b_0`
113 .. |KB| replace:: :math:`k_b`
114 .. |KDR| replace:: :math:`k_{dr}`
115 .. |NM2| replace:: (kJ mol\ :math:`^{-1}`\ nm\ :math:`^{-2}`
116 .. |NM4| replace:: (kJ mol\ :math:`^{-1}`\ nm\ :math:`^{-4}`
117 .. |DKJ| replace:: :math:`D` (kJ mol\ :math:`^{-1}`
118 .. |BETA| replace:: :math:`\beta` (nm\ :math:`^{-1}`
119 .. |C23| replace:: :math:`C_{i=2,3}` (kJ mol\ :math:`^{-1}\ nm\ :math:`^{-i}`
120 .. |BMM| replace:: :math:`b_m`
121 .. |GE0| replace:: :math:`\geq 0`
122 .. |KO| replace:: :math:`k`
123 .. |KJM| replace:: kJ mol\ :math:`^{-1}`
124 .. |LUU| replace:: low, up\ :math:`_1`,\ :math:`_2`
125 .. |MV| replace:: :math:`V`
126 .. |MW| replace:: :math:`W`
127 .. |QIJ| replace:: :math:`q_i`; :math:`q_j`
128 .. |THE0| replace:: :math:`\theta_0`
129 .. |KTHE| replace:: :math:`k_\theta`
130 .. |KJR2| replace:: kJ mol\ :math:`^{-1}`\ rad\ :math:`^{-2}`
131 .. |RN13| replace:: :math:`r_{13}`
132 .. |KUB| replace:: :math:`k_{UB}`
133 .. |C024| replace:: :math:`C_{i=0,1,2,3,4}`
134 .. |KJRI| replace:: kJ mol\ :math:`^{-1}`\ rad\ :math:`^{-i}`
135 .. |PHIS| replace:: :math:`\phi_s`
136 .. |PHI0| replace:: :math:`\phi_0`
137 .. |KPHI| replace:: :math:`k_\phi`
138 .. |PHIK| replace:: :math:`\phi,k`
139 .. |XI0| replace:: :math:`\xi_0`
140 .. |KXI| replace:: :math:`k_\xi`
141 .. |C0| replace:: :math:`C_0`
142 .. |C1| replace:: :math:`C_1`
143 .. |C2| replace:: :math:`C_2`
144 .. |C3| replace:: :math:`C_3`
145 .. |C4| replace:: :math:`C_4`
146 .. |C5| replace:: :math:`C_5`
147 .. |A0| replace:: :math:`a_0`
148 .. |A1| replace:: :math:`a_1`
149 .. |A2| replace:: :math:`a_2`
150 .. |A3| replace:: :math:`a_3`
151 .. |A4| replace:: :math:`a_4`
152 .. |DOH| replace:: :math:d_{\mbox{\sc oh}}`
153 .. |DHH| replace:: :math:d_{\mbox{\sc hh}}`
154 .. |AO| replace:: :math:`a`
155 .. |BO| replace:: :math:`b`
156 .. |CO| replace:: :math:`c`
157 .. |DO| replace:: :math:`d`
158 .. |KX| replace:: :math:`k_{x}`
159 .. |KY| replace:: :math:`k_{y}`
160 .. |KZ| replace:: :math:`k_{z}`
161 .. |GO| replace:: :math:`g`
162 .. |RO| replace:: :math:`r`
163 .. |DPHI| replace:: :math:`\Delta\phi`
164 .. |DIHR| replace:: :math:`k_{\mathrm{dihr}}`
165 .. |THET| replace:: :math:`\theta`
166 .. |NM| replace:: nm\ :math:`^{-1}`
167 .. |KC| replace:: :math:`k_c`
168 .. |THEK| replace:: :math:`\theta,k`
169 .. |R1E| replace:: :math:`r_{1e}`
170 .. |R2E| replace:: :math:`r_{2e}`
171 .. |R3E| replace:: :math:`r_{3e}`
172 .. |KRR| replace:: :math:`k_{rr'}`
173 .. |KRTH| replace:: :math:`k_{r\theta}`
174 .. |ALPH| replace:: :math:`\alpha`; |CO| (U nm\ :math:`^{\alpha}`
175 .. |UM1| replace:: U\ :math:`^{-1}`
179 .. table:: Details of ``[ moleculetype ]`` directives
181 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
182 | Name of interaction | Topology file directive | num. | func. | Order of parameters and their units | use in |
183 | | | atoms [1]_ | type [2]_ | | F.E.? [3]_ |
184 +====================================+============================+============+===========+=========================================================================+============+
185 | bond | ``bonds`` [4]_, [5]_ | 2 | 1 | |BZERO| (nm); |KB| |NM2| | all |
186 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
187 | G96 bond | ``bonds`` [4]_, [5]_ | 2 | 2 | |BZERO| (nm); |KB| |NM4| | all |
188 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
189 | Morse | ``bonds`` [4]_, [5]_ | 2 | 3 | |BZERO| (nm); |DKJ|; |BETA| | all |
190 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
191 | cubic bond | ``bonds`` [4]_, [5]_ | 2 | 4 | |BZERO| (nm); |C23| | |
192 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
193 | connection | ``bonds`` [4]_ | 2 | 5 | | |
194 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
195 | harmonic potential | ``bonds`` | 2 | 6 | |BZERO| (nm); |KB| |NM2| | all |
196 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
197 | FENE bond | ``bonds`` [4]_ | 2 | 7 | |BMM| (nm); |KB| |NM2| | |
198 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
199 | tabulated bond | ``bonds`` [4]_ | 2 | 8 | table number (|GE0|); |KO| |KJM| | |KO| |
200 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
201 | tabulated bond [6]_ | ``bonds`` | 2 | 9 | table number (|GE0|); |KO| |KJM| | |KO| |
202 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
203 | restraint potential | ``bonds`` | 2 | 10 | |LUU| (nm); |KDR| (|NM2|) | all |
204 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
205 | extra LJ or Coulomb | ``pairs`` | 2 | 1 | |MV| [7]_; |MW| [7]_ | all |
206 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
207 | extra LJ or Coulomb | ``pairs`` | 2 | 2 | fudge QQ (); |QIJ| (e), |MV| [7]_; |MW| [7]_ | |
208 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
209 | extra LJ or Coulomb | ``pairs_nb`` | 2 | 1 | |QIJ| (e); |MV| [7]_; |MW| [7]_ | |
210 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
211 | angle | ``angles`` [5]_ | 3 | 1 | |THE0| (deg); |KTHE| (|KJR2|) | all |
212 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
213 | G96 angle | ``angles`` [5]_ | 3 | 2 | |THE0| (deg); |KTHE| (|KJM|) | all |
214 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
215 | cross bond-bond | ``angles`` | 3 | 3 | |R1E|, |R2E| (nm); |KRR| (|NM2|) | |
216 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
217 | cross bond-angle | ``angles`` | 3 | 4 | |R1E|, |R2E|, |R3E| (nm); |KRTH| (|NM2|) | |
218 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
219 | Urey-Bradley | ``angles`` [5]_ | 3 | 5 | |THE0| (deg); |KTHE| (|KJR2|); |RN13| (nm); |KUB| (|NM2|) | all |
220 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
221 | quartic angle | ``angles`` [5]_ | 3 | 6 | |THE0| (deg); |C024| (|KJRI|) | |
222 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
223 | tabulated angle | ``angles`` | 3 | 8 | table number (|GE0|); |KO| (|KJM|) | |KO| |
224 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
225 | | restricted | | | | | |
226 | | bending potential | ``angles`` | 3 | 10 | |THE0| (deg); |KTHE| (|KJM|) | |
227 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
228 | proper dihedral | ``dihedrals`` | 4 | 1 | |PHIS| (deg); |KPHI| (|KJM|); multiplicity | |PHIK| |
229 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
230 | improper dihedral | ``dihedrals`` | 4 | 2 | |XI0| (deg); |KXI| (|KJR2|) | all |
231 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
232 | Ryckaert-Bellemans dihedral | ``dihedrals`` | 4 | 3 | |C0|, |C1|, |C2|, |C3|, |C4|, |C5| (|KJM|) | all |
233 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
234 | periodic improper dihedral | ``dihedrals`` | 4 | 4 | |PHIS| (deg); |KPHI| (|KJM|); multiplicity | |PHIK| |
235 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
236 | Fourier dihedral | ``dihedrals`` | 4 | 5 | |C1|, |C2|, |C3|, |C4|, |C5| (|KJM|) | all |
237 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
238 | tabulated dihedral | ``dihedrals`` | 4 | 8 | table number (|GE0|); |KO| (|KJM|) | |KO| |
239 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
240 | proper dihedral (multiple) | ``dihedrals`` | 4 | 9 | |PHIS| (deg); |KPHI| (|KJM|); multiplicity | |PHIK| |
241 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
242 | restricted dihedral | ``dihedrals`` | 4 | 10 | |PHI0| (deg); |KPHI| (|KJM|) | |
243 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
244 | combined bending-torsion potential | ``dihedrals`` | 4 | 11 | |A0|, |A1|, |A2|, |A3|, |A4| (|KJM|) | |
245 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
246 | exclusions | ``exclusions`` | 1 | | one or more atom indices | |
247 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
248 | constraint | ``constraints`` [4]_ | 2 | 1 | |BZERO| (nm) | all |
249 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
250 | constraint [6]_ | ``constraints`` | 2 | 2 | |BZERO| (nm) | all |
251 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
252 | SETTLE | ``settles`` | 1 | 1 | |DOH|, |DHH| (nm) | |
253 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
254 | 1-body virtual site | ``virtual_sites1`` | 2 | 0 | | |
255 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
256 | 2-body virtual site | ``virtual_sites2`` | 3 | 1 | |AO| () | |
257 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
258 | 2-body virtual site (fd) | ``virtual_sites2`` | 3 | 2 | |DO| (nm) | |
259 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
260 | 3-body virtual site | ``virtual_sites3`` | 4 | 1 | |AO|, |BO| () | |
261 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
262 | 3-body virtual site (fd) | ``virtual_sites3`` | 4 | 2 | |AO| (); |DO| (nm) | |
263 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
264 | 3-body virtual site (fad) | ``virtual_sites3`` | 4 | 3 | |THET| (deg); |DO| (nm) | |
265 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
266 | 3-body virtual site (out) | ``virtual_sites3`` | 4 | 4 | |AO|, |BO| (); |CO| (|NM|) | |
267 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
268 | 4-body virtual site (fdn) | ``virtual_sites4`` | 5 | 2 | |AO|, |BO| (); |CO| (nm) | |
269 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
270 | N-body virtual site (COG) | ``virtual_sitesn`` | 1 | 1 | one or more constructing atom indices | |
271 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
272 | N-body virtual site (COM) | ``virtual_sitesn`` | 1 | 2 | one or more constructing atom indices | |
273 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
274 | N-body virtual site (COW) | ``virtual_sitesn`` | 1 | 3 | | one or more pairs consisting of | |
275 | | | | | | constructing atom index and weight | |
276 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
277 | position restraint | ``position_restraints`` | 1 | 1 | |KX|, |KY|, |KZ| (|NM2|) | all |
278 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
279 | flat-bottomed position restraint | ``position_restraints`` | 1 | 2 | |GO|, |RO| (nm), |KO| (|NM2|) | |
280 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
281 | distance restraint | ``distance_restraints`` | 2 | 1 | type; label; |LUU| (nm); weight () | |
282 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
283 | dihedral restraint | ``dihedral_restraints`` | 4 | 1 | |PHI0| (deg); |DPHI| (deg); |DIHR| (|KJR2|) | all |
284 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
285 | orientation restraint | ``orientation_restraints`` | 2 | 1 | exp.; label; |ALPH|; obs. (U); weight (|UM1|) | |
286 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
287 | angle restraint | ``angle_restraints`` | 4 | 1 | |THE0| (deg); |KC| (|KJM|); multiplicity | |THEK| |
288 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
289 | angle restraint (z) | ``angle_restraints_z`` | 2 | 1 | |THE0| (deg); |KC| (|KJM|); multiplicity | |THEK| |
290 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
293 The required number of atom indices for this directive
296 The index to use to select this function type
299 Indicates which of the parameters can be interpolated in free energy calculations
302 This interaction type will be used by :ref:`grompp <gmx grompp>` for generating exclusions
305 This interaction type can be converted to constraints by :ref:`grompp <gmx grompp>`
308 The combination rule determines the type of LJ parameters, see
311 No connection, and so no exclusions, are generated for this interaction
313 Description of the file layout:
315 - Semicolon (;) and newline characters surround comments
317 - On a line ending with :math:`\backslash` the newline character is
320 - Directives are surrounded by ``[`` and ``]``
322 - The topology hierarchy (which must be followed) consists of three
325 - the parameter level, which defines certain force-field
326 specifications (see :numref:`Table %s <tab-topfile1>`)
328 - the molecule level, which should contain one or more molecule
329 definitions (see :numref:`Table %s <tab-topfile2>`)
331 - the system level, containing only system-specific information
332 (``[ system ]`` and ``[ molecules ]``)
334 - Items should be separated by spaces or tabs, not commas
336 - Atoms in molecules should be numbered consecutively starting at 1
338 - Atoms in the same charge group must be listed consecutively
340 - The file is parsed only once, which implies that no forward
341 references can be treated: items must be defined before they can be
344 - Exclusions can be generated from the bonds or overridden manually
346 - The bonded force types can be generated from the atom types or
349 - It is possible to apply multiple bonded interactions of the same type
352 - Descriptive comment lines and empty lines are highly recommended
354 - Starting with |Gromacs| version 3.1.3, all directives at the parameter
355 level can be used multiple times and there are no restrictions on the
356 order, except that an atom type needs to be defined before it can be
357 used in other parameter definitions
359 - If parameters for a certain interaction are defined multiple times
360 for the same combination of atom types the last definition is used;
361 starting with |Gromacs| version 3.1.3 :ref:`grompp <gmx grompp>` generates
362 a warning for parameter redefinitions with different values
364 - Using one of the ``[ atoms ]``,
365 ``[ bonds ]``, ``[ pairs ]``,
366 ``[ angles ]``, etc. without having used
367 ``[ moleculetype ]`` before is meaningless and generates
370 - Using ``[ molecules ]`` without having used
371 ``[ system ]`` before is meaningless and generates a
374 - After ``[ system ]`` the only allowed directive is
377 - Using an unknown string in ``[ ]`` causes all the data
378 until the next directive to be ignored and generates a warning
380 Here is an example of a topology file, ``urea.top``:
385 ; Example topology file
387 ; The force-field files to be included
388 #include "amber99.ff/forcefield.itp"
395 1 C 1 URE C 1 0.880229 12.01000 ; amber C type
396 2 O 1 URE O 2 -0.613359 16.00000 ; amber O type
397 3 N 1 URE N1 3 -0.923545 14.01000 ; amber N type
398 4 H 1 URE H11 4 0.395055 1.00800 ; amber H type
399 5 H 1 URE H12 5 0.395055 1.00800 ; amber H type
400 6 N 1 URE N2 6 -0.923545 14.01000 ; amber N type
401 7 H 1 URE H21 7 0.395055 1.00800 ; amber H type
402 8 H 1 URE H22 8 0.395055 1.00800 ; amber H type
414 ; ai aj ak al funct definition
429 [ position_restraints ]
430 ; you wouldn't normally use this for a molecule like Urea,
431 ; but we include it here for didactic purposes
433 1 1 1000 1000 1000 ; Restrain to a point
434 2 1 1000 0 1000 ; Restrain to a line (Y-axis)
435 3 1 1000 0 0 ; Restrain to a plane (Y-Z-plane)
437 [ dihedral_restraints ]
438 ; ai aj ak al type phi dphi fc
442 ; Include TIP3P water topology
443 #include "amber99/tip3p.itp"
453 Here follows the explanatory text.
455 **#include “amber99.ff/forcefield.itp” :** this includes
456 the information for the force field you are using, including bonded and
457 non-bonded parameters. This example uses the AMBER99 force field, but
458 your simulation may use a different force field. :ref:`grompp <gmx grompp>`
459 will automatically go and find this file and copy-and-paste its content.
460 That content can be seen in
461 ``share/top/amber99.ff/forcefield.itp}``, and it
470 ; nbfunc comb-rule gen-pairs fudgeLJ fudgeQQ
473 #include "ffnonbonded.itp"
474 #include "ffbonded.itp"
476 The two ``#define`` statements set up the conditions so that
477 future parts of the topology can know that the AMBER 99 force field is
482 - ``nbfunc`` is the non-bonded function type. Use 1 (Lennard-Jones) or 2
485 - ``comb-rule`` is the number of the combination rule (see :ref:`nbpar`).
487 - ``gen-pairs`` is for pair generation. The default is
488 ‘no’, *i.e.* get 1-4 parameters from the pairtypes list. When
489 parameters are not present in the list, stop with a fatal error.
490 Setting ‘yes’ generates 1-4 parameters that are not present in the
491 pair list from normal Lennard-Jones parameters using
494 - ``fudgeLJ`` is the factor by which to multiply
495 Lennard-Jones 1-4 interactions, default 1
497 - ``fudgeQQ`` is the factor by which to multiply
498 electrostatic 1-4 interactions, default 1
500 - :math:`N` is the power for the repulsion term in a 6-\ :math:`N`
501 potential (with nonbonded-type Lennard-Jones only), starting with
502 |Gromacs| version 4.5, :ref:`grompp <gmx mdrun>` also reads and applies
503 :math:`N`, for values not equal to 12 tabulated interaction functions
504 are used (in older version you would have to use user tabulated
507 **Note** that ``gen-pairs``, ``fudgeLJ``,
508 ``fudgeQQ``, and :math:`N` are optional.
509 ``fudgeLJ`` is only used when generate pairs is set to
510 ‘yes’, and ``fudgeQQ`` is always used. However, if you want
511 to specify :math:`N` you need to give a value for the other parameters
514 Then some other ``#include`` statements add in the large
515 amount of data needed to describe the rest of the force field. We will
516 skip these and return to ``urea.top``. There we will see
518 **[ moleculetype ] :** defines the name of your molecule
519 in this :ref:`top` and nrexcl = 3 stands for excluding
520 non-bonded interactions between atoms that are no further than 3 bonds
523 **[ atoms ] :** defines the molecule, where
524 ``nr`` and ``type`` are fixed, the rest is user
525 defined. So ``atom`` can be named as you like,
526 ``cgnr`` made larger or smaller (if possible, the total
527 charge of a charge group should be zero), and charges can be changed
530 **[ bonds ] :** no comment.
532 **[ pairs ] :** LJ and Coulomb 1-4 interactions
534 **[ angles ] :** no comment
536 **[ dihedrals ] :** in this case there are 9 proper
537 dihedrals (funct = 1), 3 improper (funct = 4) and no Ryckaert-Bellemans
538 type dihedrals. If you want to include Ryckaert-Bellemans type dihedrals
539 in a topology, do the following (in case of *e.g.* decane):
544 ; ai aj ak al funct c0 c1 c2
548 In the original implementation of the potential for
549 alkanes \ :ref:`131 <refRyckaert78>` no 1-4 interactions were used, which means that in
550 order to implement that particular force field you need to remove the
551 1-4 interactions from the ``[ pairs ]`` section of your
552 topology. In most modern force fields, like OPLS/AA or Amber the rules
553 are different, and the Ryckaert-Bellemans potential is used as a cosine
554 series in combination with 1-4 interactions.
556 **[ position_restraints ] :** harmonically restrain the selected particles to reference
557 positions (:ref:`positionrestraint`). The reference positions are read
558 from a separate coordinate file by :ref:`grompp <gmx grompp>`.
560 **[ dihedral_restraints ] :** restrain selected dihedrals to a reference value. The
561 implementation of dihedral restraints is described in section
562 :ref:`dihedralrestraint` of the manual. The parameters specified in
563 the ``[dihedral_restraints]`` directive are as follows:
565 - ``type`` has only one possible value which is 1
567 - ``phi`` is the value of :math:`\phi_0` in :eq:`eqn. %s <eqndphi>` and
568 :eq:`eqn. %s <eqndihre>` of the manual.
570 - ``dphi`` is the value of :math:`\Delta\phi` in :eq:`eqn. %s <eqndihre>` of the
573 - ``fc`` is the force constant :math:`k_{dihr}` in :eq:`eqn. %s <eqndihre>` of the
576 **#include “tip3p.itp” :** includes a topology file that was already
577 constructed (see section :ref:`molitp`).
579 **[ system ] :** title of your system, user-defined
581 **[ molecules ] :** this defines the total number of (sub)molecules in your system
582 that are defined in this :ref:`top`. In this example file, it stands for 1
583 urea molecule dissolved in 1000 water molecules. The molecule type ``SOL``
584 is defined in the ``tip3p.itp`` file. Each name here must correspond to a
585 name given with ``[ moleculetype ]`` earlier in the topology. The order of the blocks of
586 molecule types and the numbers of such molecules must match the
587 coordinate file that accompanies the topology when supplied to :ref:`grompp <gmx grompp>`.
588 The blocks of molecules do not need to be contiguous, but some tools
589 (e.g. :ref:`genion <gmx genion>`) may act only on the first or last such block of a
590 particular molecule type. Also, these blocks have nothing to do with the
591 definition of groups (see sec. :ref:`groupconcept` and
592 sec. :ref:`usinggroups`).
599 If you construct a topology file you will use frequently (like the water
600 molecule, ``tip3p.itp``, which is already constructed for
601 you) it is good to make a ``molecule.itp`` file. This only
602 lists the information of one particular molecule and allows you to
603 re-use the ``[ moleculetype ]`` in multiple systems without
604 re-invoking :ref:`pdb2gmx <gmx pdb2gmx>` or manually copying and pasting. An
605 example ``urea.itp`` follows:
614 1 C 1 URE C 1 0.880229 12.01000 ; amber C type
616 8 H 1 URE H22 8 0.395055 1.00800 ; amber H type
623 ; ai aj ak al funct definition
632 Using :ref:`itp` files results in a very short
638 ; Example topology file
640 ; The force field files to be included
641 #include "amber99.ff/forcefield.itp"
645 ; Include TIP3P water topology
646 #include "amber99/tip3p.itp"
659 A very powerful feature in |Gromacs| is the use of ``#ifdef``
660 statements in your :ref:`top` file. By making use of this
661 statement, and associated ``#define`` statements like were
662 seen in ``amber99.ff/forcefield.itp`` earlier,
663 different parameters for one molecule can be used in the same
664 :ref:`top` file. An example is given for TFE, where there is
665 an option to use different charges on the atoms: charges derived by De
666 Loof et al. :ref:`132 <refLoof92>` or by Van Buuren and
667 Berendsen \ :ref:`133 <refBuuren93a>`. In fact, you can use much of the
668 functionality of the C preprocessor, ``cpp``, because
669 :ref:`grompp <gmx grompp>` contains similar pre-processing functions to scan
670 the file. The way to make use of the ``#ifdef`` option is as
673 - either use the option ``define = -DDeLoof`` in the
674 :ref:`mdp` file (containing :ref:`grompp <gmx grompp>` input
675 parameters), or use the line ``#define DeLoof`` early in
676 your :ref:`top` or :ref:`itp` file; and
678 - put the ``#ifdef`` statements in your
679 :ref:`top`, as shown below:
689 ; nr type resnr residu atom cgnr charge mass
691 ; Use Charges from DeLoof
696 5 CH2 1 TFE CH2 1 0.25
697 6 OA 1 TFE OA 1 -0.65
700 ; Use Charges from VanBuuren
705 5 CH2 1 TFE CH2 1 0.26
706 6 OA 1 TFE OA 1 -0.55
712 6 7 1 1.000000e-01 3.138000e+05
713 1 2 1 1.360000e-01 4.184000e+05
714 1 3 1 1.360000e-01 4.184000e+05
715 1 4 1 1.360000e-01 4.184000e+05
716 1 5 1 1.530000e-01 3.347000e+05
717 5 6 1 1.430000e-01 3.347000e+05
720 This mechanism is used by :ref:`pdb2gmx <gmx pdb2gmx>` to implement optional position
721 restraints (:ref:`positionrestraint`) by ``#include``-ing an :ref:`itp` file
722 whose contents will be meaningful only if a particular ``#define`` is set
723 (and spelled correctly!)
725 Topologies for free energy calculations
726 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
728 Free energy differences between two systems, A and B, can be calculated
729 as described in sec. :ref:`fecalc`. Systems A and B are described by
730 topologies consisting of the same number of molecules with the same
731 number of atoms. Masses and non-bonded interactions can be perturbed by
732 adding B parameters under the ``[ atoms ]`` directive. Bonded interactions can be
733 perturbed by adding B parameters to the bonded types or the bonded
734 interactions. The parameters that can be perturbed are listed in
735 :numref:`Tables %s <tab-topfile1>` and :numref:`%s <tab-topfile2>`.
736 The :math:`\lambda`-dependence of the
737 interactions is described in section sec. :ref:`feia`. The bonded
738 parameters that are used (on the line of the bonded interaction
739 definition, or the ones looked up on atom types in the bonded type
740 lists) is explained in :numref:`Table %s <tab-topfe>`. In most cases, things should
741 work intuitively. When the A and B atom types in a bonded interaction
742 are not all identical and parameters are not present for the B-state,
743 either on the line or in the bonded types, :ref:`grompp <gmx grompp>` uses the A-state
744 parameters and issues a warning. For free energy calculations, all or no
745 parameters for topology B (:math:`\lambda = 1`) should be added on the
746 same line, after the normal parameters, in the same order as the normal
747 parameters. From |Gromacs| 4.6 onward, if :math:`\lambda` is treated as a
748 vector, then the ``bonded-lambdas`` component controls all bonded terms that
749 are not explicitly labeled as restraints. Restrain terms are controlled
750 by the ``restraint-lambdas`` component.
752 .. |NOT| replace:: :math:`-`
756 .. table:: The bonded parameters that are used for free energy topologies,
757 on the line of the bonded interaction definition or looked up
758 in the bond types section based on atom types. A and B indicate the
759 parameters used for state A and B respectively, + and |NOT| indicate
760 the (non-)presence of parameters in the topology, x indicates that
761 the presence has no influence.
763 +--------------------+---------------+---------------------------------+---------+
764 | B-state atom types | parameters | parameters in bonded types | |
765 + + +-----------------+---------------+ +
766 | all identical to | on line | A atom types | B atom types | message |
767 + +-------+-------+-------+---------+-------+-------+ +
768 | A-state atom types | A | B | A | B | A | B | |
769 +====================+=======+=======+=======+=========+=======+=======+=========+
770 | | +AB | |NOT| | x | x | | | |
771 | | +A | +B | x | x | | | |
772 | yes | |NOT| | |NOT| | |NOT| | |NOT| | | | error |
773 | | |NOT| | |NOT| | +AB | |NOT| | | | |
774 | | |NOT| | |NOT| | +A | +B | | | |
775 +--------------------+-------+-------+-------+---------+-------+-------+---------+
776 | | +AB | |NOT| | x | x | x | x | warning |
777 | | +A | +B | x | x | x | x | |
778 | | |NOT| | |NOT| | |NOT| | |NOT| | x | x | error |
779 | no | |NOT| | |NOT| | +AB | |NOT| | |NOT| | |NOT| | warning |
780 | | |NOT| | |NOT| | +A | +B | |NOT| | |NOT| | warning |
781 | | |NOT| | |NOT| | +A | x | +B | |NOT| | |
782 | | |NOT| | |NOT| | +A | x | + | +B | |
783 +--------------------+-------+-------+-------+---------+-------+-------+---------+
787 Below is an example of a topology which changes from 200 propanols to
788 200 pentanes using the GROMOS-96 force field.
793 ; Include force field parameters
794 #include "gromos43a1.ff/forcefield.itp"
801 ; nr type resnr residue atom cgnr charge mass typeB chargeB massB
802 1 H 1 PROP PH 1 0.398 1.008 CH3 0.0 15.035
803 2 OA 1 PROP PO 1 -0.548 15.9994 CH2 0.0 14.027
804 3 CH2 1 PROP PC1 1 0.150 14.027 CH2 0.0 14.027
805 4 CH2 1 PROP PC2 2 0.000 14.027
806 5 CH3 1 PROP PC3 2 0.000 15.035
809 ; ai aj funct par_A par_B
821 ; ai aj ak funct par_A par_B
827 ; ai aj ak al funct par_A par_B
828 1 2 3 4 1 gd_12 gd_17
829 2 3 4 5 1 gd_17 gd_17
839 Atoms that are not perturbed, ``PC2`` and
840 ``PC3``, do not need B-state parameter specifications, since
841 the B parameters will be copied from the A parameters. Bonded
842 interactions between atoms that are not perturbed do not need B
843 parameter specifications, as is the case for the last bond in the
844 example topology. Topologies using the OPLS/AA force field need no
845 bonded parameters at all, since both the A and B parameters are
846 determined by the atom types. Non-bonded interactions involving one or
847 two perturbed atoms use the free-energy perturbation functional forms.
848 Non-bonded interactions between two non-perturbed atoms use the normal
849 functional forms. This means that when, for instance, only the charge of
850 a particle is perturbed, its Lennard-Jones interactions will also be
851 affected when lambda is not equal to zero or one.
853 **Note** that this topology uses the GROMOS-96 force field, in which the
854 bonded interactions are not determined by the atom types. The bonded
855 interaction strings are converted by the C-preprocessor. The force-field
856 parameter files contain lines like:
860 #define gb_26 0.1530 7.1500e+06
862 #define gd_17 0.000 5.86 3
869 | The constraint force between two atoms in one molecule can be
870 calculated with the free energy perturbation code by adding a
871 constraint between the two atoms, with a different length in the A and
872 B topology. When the B length is 1 nm longer than the A length and
873 lambda is kept constant at zero, the derivative of the Hamiltonian
874 with respect to lambda is the constraint force. For constraints
875 between molecules, the pull code can be used, see sec. :ref:`pull`.
876 Below is an example for calculating the constraint force at 0.7 nm
877 between two methanes in water, by combining the two methanes into one
878 “molecule.” **Note** that the definition of a “molecule” in |Gromacs|
879 does not necessarily correspond to the chemical definition of a
880 molecule. In |Gromacs|, a “molecule” can be defined as any group of
881 atoms that one wishes to consider simultaneously. The added constraint
882 is of function type 2, which means that it is not used for generating
883 exclusions (see sec. :ref:`excl`). Note that the constraint free energy
884 term is included in the derivative term, and is specifically included
885 in the ``bonded-lambdas`` component. However, the free energy for changing
886 constraints is *not* included in the potential energy differences used
887 for BAR and MBAR, as this requires reevaluating the energy at each of
888 the constraint components. This functionality is planned for later
893 ; Include force-field parameters
894 #include "gromos43a1.ff/forcefield.itp"
901 ; nr type resnr residu atom cgnr charge mass
902 1 CH4 1 CH4 C1 1 0 16.043
903 2 CH4 1 CH4 C2 2 0 16.043
905 ; ai aj funct length_A length_B
908 #include "gromos43a1.ff/spc.itp"
922 Files with the :ref:`gro` file extension contain a molecular
923 structure in GROMOS-87 format. A sample piece is included below:
927 MD of 2 waters, reformat step, PA aug-91
929 1WATER OW1 1 0.126 1.624 1.679 0.1227 -0.0580 0.0434
930 1WATER HW2 2 0.190 1.661 1.747 0.8085 0.3191 -0.7791
931 1WATER HW3 3 0.177 1.568 1.613 -0.9045 -2.6469 1.3180
932 2WATER OW1 4 1.275 0.053 0.622 0.2519 0.3140 -0.1734
933 2WATER HW2 5 1.337 0.002 0.680 -1.0641 -1.1349 0.0257
934 2WATER HW3 6 1.326 0.120 0.568 1.9427 -0.8216 -0.0244
935 1.82060 1.82060 1.82060
937 This format is fixed, *i.e.* all columns are in a fixed position. If you
938 want to read such a file in your own program without using the |Gromacs|
939 libraries you can use the following formats:
942 ``“%5i%5s%5s%5i%8.3f%8.3f%8.3f%8.4f%8.4f%8.4f”``
944 Or to be more precise, with title *etc.* it looks like this:
950 for (i=0; (i<natoms); i++) {
951 "%5d%-5s%5s%5d%8.3f%8.3f%8.3f%8.4f%8.4f%8.4f\n",
952 residuenr,residuename,atomname,atomnr,x,y,z,vx,vy,vz
954 "%10.5f%10.5f%10.5f%10.5f%10.5f%10.5f%10.5f%10.5f%10.5f\n",
955 box[X][X],box[Y][Y],box[Z][Z],
956 box[X][Y],box[X][Z],box[Y][X],box[Y][Z],box[Z][X],box[Z][Y]
959 ``(i5,2a5,i5,3f8.3,3f8.4)``
961 So ``confin.gro`` is the |Gromacs| coordinate file and is
962 almost the same as the GROMOS-87 file (for GROMOS users: when used with
963 ``ntx=7``). The only difference is the box for which |Gromacs|
964 uses a tensor, not a vector.