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 | 2-body virtual site | ``virtual_sites2`` | 3 | 1 | |AO| () | |
255 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
256 | 2-body virtual site (fd) | ``virtual_sites2`` | 3 | 2 | |DO| (nm) | |
257 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
258 | 3-body virtual site | ``virtual_sites3`` | 4 | 1 | |AO|, |BO| () | |
259 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
260 | 3-body virtual site (fd) | ``virtual_sites3`` | 4 | 2 | |AO| (); |DO| (nm) | |
261 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
262 | 3-body virtual site (fad) | ``virtual_sites3`` | 4 | 3 | |THET| (deg); |DO| (nm) | |
263 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
264 | 3-body virtual site (out) | ``virtual_sites3`` | 4 | 4 | |AO|, |BO| (); |CO| (|NM|) | |
265 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
266 | 4-body virtual site (fdn) | ``virtual_sites4`` | 5 | 2 | |AO|, |BO| (); |CO| (nm) | |
267 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
268 | N-body virtual site (COG) | ``virtual_sitesn`` | 1 | 1 | one or more constructing atom indices | |
269 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
270 | N-body virtual site (COM) | ``virtual_sitesn`` | 1 | 2 | one or more constructing atom indices | |
271 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
272 | N-body virtual site (COW) | ``virtual_sitesn`` | 1 | 3 | | one or more pairs consisting of | |
273 | | | | | | constructing atom index and weight | |
274 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
275 | position restraint | ``position_restraints`` | 1 | 1 | |KX|, |KY|, |KZ| (|NM2|) | all |
276 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
277 | flat-bottomed position restraint | ``position_restraints`` | 1 | 2 | |GO|, |RO| (nm), |KO| (|NM2|) | |
278 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
279 | distance restraint | ``distance_restraints`` | 2 | 1 | type; label; |LUU| (nm); weight () | |
280 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
281 | dihedral restraint | ``dihedral_restraints`` | 4 | 1 | |PHI0| (deg); |DPHI| (deg); |DIHR| (|KJR2|) | all |
282 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
283 | orientation restraint | ``orientation_restraints`` | 2 | 1 | exp.; label; |ALPH|; obs. (U); weight (|UM1|) | |
284 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
285 | angle restraint | ``angle_restraints`` | 4 | 1 | |THE0| (deg); |KC| (|KJM|); multiplicity | |THEK| |
286 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
287 | angle restraint (z) | ``angle_restraints_z`` | 2 | 1 | |THE0| (deg); |KC| (|KJM|); multiplicity | |THEK| |
288 +------------------------------------+----------------------------+------------+-----------+-------------------------------------------------------------------------+------------+
291 The required number of atom indices for this directive
294 The index to use to select this function type
297 Indicates which of the parameters can be interpolated in free energy calculations
300 This interaction type will be used by :ref:`grompp <gmx grompp>` for generating exclusions
303 This interaction type can be converted to constraints by :ref:`grompp <gmx grompp>`
306 The combination rule determines the type of LJ parameters, see
309 No connection, and so no exclusions, are generated for this interaction
311 Description of the file layout:
313 - Semicolon (;) and newline characters surround comments
315 - On a line ending with :math:`\backslash` the newline character is
318 - Directives are surrounded by ``[`` and ``]``
320 - The topology hierarchy (which must be followed) consists of three
323 - the parameter level, which defines certain force-field
324 specifications (see :numref:`Table %s <tab-topfile1>`)
326 - the molecule level, which should contain one or more molecule
327 definitions (see :numref:`Table %s <tab-topfile2>`)
329 - the system level, containing only system-specific information
330 (``[ system ]`` and ``[ molecules ]``)
332 - Items should be separated by spaces or tabs, not commas
334 - Atoms in molecules should be numbered consecutively starting at 1
336 - Atoms in the same charge group must be listed consecutively
338 - The file is parsed only once, which implies that no forward
339 references can be treated: items must be defined before they can be
342 - Exclusions can be generated from the bonds or overridden manually
344 - The bonded force types can be generated from the atom types or
347 - It is possible to apply multiple bonded interactions of the same type
350 - Descriptive comment lines and empty lines are highly recommended
352 - Starting with |Gromacs| version 3.1.3, all directives at the parameter
353 level can be used multiple times and there are no restrictions on the
354 order, except that an atom type needs to be defined before it can be
355 used in other parameter definitions
357 - If parameters for a certain interaction are defined multiple times
358 for the same combination of atom types the last definition is used;
359 starting with |Gromacs| version 3.1.3 :ref:`grompp <gmx grompp>` generates
360 a warning for parameter redefinitions with different values
362 - Using one of the ``[ atoms ]``,
363 ``[ bonds ]``, ``[ pairs ]``,
364 ``[ angles ]``, etc. without having used
365 ``[ moleculetype ]`` before is meaningless and generates
368 - Using ``[ molecules ]`` without having used
369 ``[ system ]`` before is meaningless and generates a
372 - After ``[ system ]`` the only allowed directive is
375 - Using an unknown string in ``[ ]`` causes all the data
376 until the next directive to be ignored and generates a warning
378 Here is an example of a topology file, ``urea.top``:
383 ; Example topology file
385 ; The force-field files to be included
386 #include "amber99.ff/forcefield.itp"
393 1 C 1 URE C 1 0.880229 12.01000 ; amber C type
394 2 O 1 URE O 2 -0.613359 16.00000 ; amber O type
395 3 N 1 URE N1 3 -0.923545 14.01000 ; amber N type
396 4 H 1 URE H11 4 0.395055 1.00800 ; amber H type
397 5 H 1 URE H12 5 0.395055 1.00800 ; amber H type
398 6 N 1 URE N2 6 -0.923545 14.01000 ; amber N type
399 7 H 1 URE H21 7 0.395055 1.00800 ; amber H type
400 8 H 1 URE H22 8 0.395055 1.00800 ; amber H type
412 ; ai aj ak al funct definition
427 [ position_restraints ]
428 ; you wouldn't normally use this for a molecule like Urea,
429 ; but we include it here for didactic purposes
431 1 1 1000 1000 1000 ; Restrain to a point
432 2 1 1000 0 1000 ; Restrain to a line (Y-axis)
433 3 1 1000 0 0 ; Restrain to a plane (Y-Z-plane)
435 [ dihedral_restraints ]
436 ; ai aj ak al type phi dphi fc
440 ; Include TIP3P water topology
441 #include "amber99/tip3p.itp"
451 Here follows the explanatory text.
453 **#include “amber99.ff/forcefield.itp” :** this includes
454 the information for the force field you are using, including bonded and
455 non-bonded parameters. This example uses the AMBER99 force field, but
456 your simulation may use a different force field. :ref:`grompp <gmx grompp>`
457 will automatically go and find this file and copy-and-paste its content.
458 That content can be seen in
459 ``share/top/amber99.ff/forcefield.itp}``, and it
468 ; nbfunc comb-rule gen-pairs fudgeLJ fudgeQQ
471 #include "ffnonbonded.itp"
472 #include "ffbonded.itp"
474 The two ``#define`` statements set up the conditions so that
475 future parts of the topology can know that the AMBER 99 force field is
480 - ``nbfunc`` is the non-bonded function type. Use 1 (Lennard-Jones) or 2
483 - ``comb-rule`` is the number of the combination rule (see :ref:`nbpar`).
485 - ``gen-pairs`` is for pair generation. The default is
486 ‘no’, *i.e.* get 1-4 parameters from the pairtypes list. When
487 parameters are not present in the list, stop with a fatal error.
488 Setting ‘yes’ generates 1-4 parameters that are not present in the
489 pair list from normal Lennard-Jones parameters using
492 - ``fudgeLJ`` is the factor by which to multiply
493 Lennard-Jones 1-4 interactions, default 1
495 - ``fudgeQQ`` is the factor by which to multiply
496 electrostatic 1-4 interactions, default 1
498 - :math:`N` is the power for the repulsion term in a 6-\ :math:`N`
499 potential (with nonbonded-type Lennard-Jones only), starting with
500 |Gromacs| version 4.5, :ref:`grompp <gmx mdrun>` also reads and applies
501 :math:`N`, for values not equal to 12 tabulated interaction functions
502 are used (in older version you would have to use user tabulated
505 **Note** that ``gen-pairs``, ``fudgeLJ``,
506 ``fudgeQQ``, and :math:`N` are optional.
507 ``fudgeLJ`` is only used when generate pairs is set to
508 ‘yes’, and ``fudgeQQ`` is always used. However, if you want
509 to specify :math:`N` you need to give a value for the other parameters
512 Then some other ``#include`` statements add in the large
513 amount of data needed to describe the rest of the force field. We will
514 skip these and return to ``urea.top``. There we will see
516 **[ moleculetype ] :** defines the name of your molecule
517 in this :ref:`top` and nrexcl = 3 stands for excluding
518 non-bonded interactions between atoms that are no further than 3 bonds
521 **[ atoms ] :** defines the molecule, where
522 ``nr`` and ``type`` are fixed, the rest is user
523 defined. So ``atom`` can be named as you like,
524 ``cgnr`` made larger or smaller (if possible, the total
525 charge of a charge group should be zero), and charges can be changed
528 **[ bonds ] :** no comment.
530 **[ pairs ] :** LJ and Coulomb 1-4 interactions
532 **[ angles ] :** no comment
534 **[ dihedrals ] :** in this case there are 9 proper
535 dihedrals (funct = 1), 3 improper (funct = 4) and no Ryckaert-Bellemans
536 type dihedrals. If you want to include Ryckaert-Bellemans type dihedrals
537 in a topology, do the following (in case of *e.g.* decane):
542 ; ai aj ak al funct c0 c1 c2
546 In the original implementation of the potential for
547 alkanes \ :ref:`131 <refRyckaert78>` no 1-4 interactions were used, which means that in
548 order to implement that particular force field you need to remove the
549 1-4 interactions from the ``[ pairs ]`` section of your
550 topology. In most modern force fields, like OPLS/AA or Amber the rules
551 are different, and the Ryckaert-Bellemans potential is used as a cosine
552 series in combination with 1-4 interactions.
554 **[ position_restraints ] :** harmonically restrain the selected particles to reference
555 positions (:ref:`positionrestraint`). The reference positions are read
556 from a separate coordinate file by :ref:`grompp <gmx grompp>`.
558 **[ dihedral_restraints ] :** restrain selected dihedrals to a reference value. The
559 implementation of dihedral restraints is described in section
560 :ref:`dihedralrestraint` of the manual. The parameters specified in
561 the ``[dihedral_restraints]`` directive are as follows:
563 - ``type`` has only one possible value which is 1
565 - ``phi`` is the value of :math:`\phi_0` in :eq:`eqn. %s <eqndphi>` and
566 :eq:`eqn. %s <eqndihre>` of the manual.
568 - ``dphi`` is the value of :math:`\Delta\phi` in :eq:`eqn. %s <eqndihre>` of the
571 - ``fc`` is the force constant :math:`k_{dihr}` in :eq:`eqn. %s <eqndihre>` of the
574 **#include “tip3p.itp” :** includes a topology file that was already
575 constructed (see section :ref:`molitp`).
577 **[ system ] :** title of your system, user-defined
579 **[ molecules ] :** this defines the total number of (sub)molecules in your system
580 that are defined in this :ref:`top`. In this example file, it stands for 1
581 urea molecule dissolved in 1000 water molecules. The molecule type ``SOL``
582 is defined in the ``tip3p.itp`` file. Each name here must correspond to a
583 name given with ``[ moleculetype ]`` earlier in the topology. The order of the blocks of
584 molecule types and the numbers of such molecules must match the
585 coordinate file that accompanies the topology when supplied to :ref:`grompp <gmx grompp>`.
586 The blocks of molecules do not need to be contiguous, but some tools
587 (e.g. :ref:`genion <gmx genion>`) may act only on the first or last such block of a
588 particular molecule type. Also, these blocks have nothing to do with the
589 definition of groups (see sec. :ref:`groupconcept` and
590 sec. :ref:`usinggroups`).
597 If you construct a topology file you will use frequently (like the water
598 molecule, ``tip3p.itp``, which is already constructed for
599 you) it is good to make a ``molecule.itp`` file. This only
600 lists the information of one particular molecule and allows you to
601 re-use the ``[ moleculetype ]`` in multiple systems without
602 re-invoking :ref:`pdb2gmx <gmx pdb2gmx>` or manually copying and pasting. An
603 example ``urea.itp`` follows:
612 1 C 1 URE C 1 0.880229 12.01000 ; amber C type
614 8 H 1 URE H22 8 0.395055 1.00800 ; amber H type
621 ; ai aj ak al funct definition
630 Using :ref:`itp` files results in a very short
636 ; Example topology file
638 ; The force field files to be included
639 #include "amber99.ff/forcefield.itp"
643 ; Include TIP3P water topology
644 #include "amber99/tip3p.itp"
657 A very powerful feature in |Gromacs| is the use of ``#ifdef``
658 statements in your :ref:`top` file. By making use of this
659 statement, and associated ``#define`` statements like were
660 seen in ``amber99.ff/forcefield.itp`` earlier,
661 different parameters for one molecule can be used in the same
662 :ref:`top` file. An example is given for TFE, where there is
663 an option to use different charges on the atoms: charges derived by De
664 Loof et al. :ref:`132 <refLoof92>` or by Van Buuren and
665 Berendsen \ :ref:`133 <refBuuren93a>`. In fact, you can use much of the
666 functionality of the C preprocessor, ``cpp``, because
667 :ref:`grompp <gmx grompp>` contains similar pre-processing functions to scan
668 the file. The way to make use of the ``#ifdef`` option is as
671 - either use the option ``define = -DDeLoof`` in the
672 :ref:`mdp` file (containing :ref:`grompp <gmx grompp>` input
673 parameters), or use the line ``#define DeLoof`` early in
674 your :ref:`top` or :ref:`itp` file; and
676 - put the ``#ifdef`` statements in your
677 :ref:`top`, as shown below:
687 ; nr type resnr residu atom cgnr charge mass
689 ; Use Charges from DeLoof
694 5 CH2 1 TFE CH2 1 0.25
695 6 OA 1 TFE OA 1 -0.65
698 ; Use Charges from VanBuuren
703 5 CH2 1 TFE CH2 1 0.26
704 6 OA 1 TFE OA 1 -0.55
710 6 7 1 1.000000e-01 3.138000e+05
711 1 2 1 1.360000e-01 4.184000e+05
712 1 3 1 1.360000e-01 4.184000e+05
713 1 4 1 1.360000e-01 4.184000e+05
714 1 5 1 1.530000e-01 3.347000e+05
715 5 6 1 1.430000e-01 3.347000e+05
718 This mechanism is used by :ref:`pdb2gmx <gmx pdb2gmx>` to implement optional position
719 restraints (:ref:`positionrestraint`) by ``#include``-ing an :ref:`itp` file
720 whose contents will be meaningful only if a particular ``#define`` is set
721 (and spelled correctly!)
723 Topologies for free energy calculations
724 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
726 Free energy differences between two systems, A and B, can be calculated
727 as described in sec. :ref:`fecalc`. Systems A and B are described by
728 topologies consisting of the same number of molecules with the same
729 number of atoms. Masses and non-bonded interactions can be perturbed by
730 adding B parameters under the ``[ atoms ]`` directive. Bonded interactions can be
731 perturbed by adding B parameters to the bonded types or the bonded
732 interactions. The parameters that can be perturbed are listed in
733 :numref:`Tables %s <tab-topfile1>` and :numref:`%s <tab-topfile2>`.
734 The :math:`\lambda`-dependence of the
735 interactions is described in section sec. :ref:`feia`. The bonded
736 parameters that are used (on the line of the bonded interaction
737 definition, or the ones looked up on atom types in the bonded type
738 lists) is explained in :numref:`Table %s <tab-topfe>`. In most cases, things should
739 work intuitively. When the A and B atom types in a bonded interaction
740 are not all identical and parameters are not present for the B-state,
741 either on the line or in the bonded types, :ref:`grompp <gmx grompp>` uses the A-state
742 parameters and issues a warning. For free energy calculations, all or no
743 parameters for topology B (:math:`\lambda = 1`) should be added on the
744 same line, after the normal parameters, in the same order as the normal
745 parameters. From |Gromacs| 4.6 onward, if :math:`\lambda` is treated as a
746 vector, then the ``bonded-lambdas`` component controls all bonded terms that
747 are not explicitly labeled as restraints. Restrain terms are controlled
748 by the ``restraint-lambdas`` component.
750 .. |NOT| replace:: :math:`-`
754 .. table:: The bonded parameters that are used for free energy topologies,
755 on the line of the bonded interaction definition or looked up
756 in the bond types section based on atom types. A and B indicate the
757 parameters used for state A and B respectively, + and |NOT| indicate
758 the (non-)presence of parameters in the topology, x indicates that
759 the presence has no influence.
761 +--------------------+---------------+---------------------------------+---------+
762 | B-state atom types | parameters | parameters in bonded types | |
763 + + +-----------------+---------------+ +
764 | all identical to | on line | A atom types | B atom types | message |
765 + +-------+-------+-------+---------+-------+-------+ +
766 | A-state atom types | A | B | A | B | A | B | |
767 +====================+=======+=======+=======+=========+=======+=======+=========+
768 | | +AB | |NOT| | x | x | | | |
769 | | +A | +B | x | x | | | |
770 | yes | |NOT| | |NOT| | |NOT| | |NOT| | | | error |
771 | | |NOT| | |NOT| | +AB | |NOT| | | | |
772 | | |NOT| | |NOT| | +A | +B | | | |
773 +--------------------+-------+-------+-------+---------+-------+-------+---------+
774 | | +AB | |NOT| | x | x | x | x | warning |
775 | | +A | +B | x | x | x | x | |
776 | | |NOT| | |NOT| | |NOT| | |NOT| | x | x | error |
777 | no | |NOT| | |NOT| | +AB | |NOT| | |NOT| | |NOT| | warning |
778 | | |NOT| | |NOT| | +A | +B | |NOT| | |NOT| | warning |
779 | | |NOT| | |NOT| | +A | x | +B | |NOT| | |
780 | | |NOT| | |NOT| | +A | x | + | +B | |
781 +--------------------+-------+-------+-------+---------+-------+-------+---------+
785 Below is an example of a topology which changes from 200 propanols to
786 200 pentanes using the GROMOS-96 force field.
791 ; Include force field parameters
792 #include "gromos43a1.ff/forcefield.itp"
799 ; nr type resnr residue atom cgnr charge mass typeB chargeB massB
800 1 H 1 PROP PH 1 0.398 1.008 CH3 0.0 15.035
801 2 OA 1 PROP PO 1 -0.548 15.9994 CH2 0.0 14.027
802 3 CH2 1 PROP PC1 1 0.150 14.027 CH2 0.0 14.027
803 4 CH2 1 PROP PC2 2 0.000 14.027
804 5 CH3 1 PROP PC3 2 0.000 15.035
807 ; ai aj funct par_A par_B
819 ; ai aj ak funct par_A par_B
825 ; ai aj ak al funct par_A par_B
826 1 2 3 4 1 gd_12 gd_17
827 2 3 4 5 1 gd_17 gd_17
837 Atoms that are not perturbed, ``PC2`` and
838 ``PC3``, do not need B-state parameter specifications, since
839 the B parameters will be copied from the A parameters. Bonded
840 interactions between atoms that are not perturbed do not need B
841 parameter specifications, as is the case for the last bond in the
842 example topology. Topologies using the OPLS/AA force field need no
843 bonded parameters at all, since both the A and B parameters are
844 determined by the atom types. Non-bonded interactions involving one or
845 two perturbed atoms use the free-energy perturbation functional forms.
846 Non-bonded interactions between two non-perturbed atoms use the normal
847 functional forms. This means that when, for instance, only the charge of
848 a particle is perturbed, its Lennard-Jones interactions will also be
849 affected when lambda is not equal to zero or one.
851 **Note** that this topology uses the GROMOS-96 force field, in which the
852 bonded interactions are not determined by the atom types. The bonded
853 interaction strings are converted by the C-preprocessor. The force-field
854 parameter files contain lines like:
858 #define gb_26 0.1530 7.1500e+06
860 #define gd_17 0.000 5.86 3
867 | The constraint force between two atoms in one molecule can be
868 calculated with the free energy perturbation code by adding a
869 constraint between the two atoms, with a different length in the A and
870 B topology. When the B length is 1 nm longer than the A length and
871 lambda is kept constant at zero, the derivative of the Hamiltonian
872 with respect to lambda is the constraint force. For constraints
873 between molecules, the pull code can be used, see sec. :ref:`pull`.
874 Below is an example for calculating the constraint force at 0.7 nm
875 between two methanes in water, by combining the two methanes into one
876 “molecule.” **Note** that the definition of a “molecule” in |Gromacs|
877 does not necessarily correspond to the chemical definition of a
878 molecule. In |Gromacs|, a “molecule” can be defined as any group of
879 atoms that one wishes to consider simultaneously. The added constraint
880 is of function type 2, which means that it is not used for generating
881 exclusions (see sec. :ref:`excl`). Note that the constraint free energy
882 term is included in the derivative term, and is specifically included
883 in the ``bonded-lambdas`` component. However, the free energy for changing
884 constraints is *not* included in the potential energy differences used
885 for BAR and MBAR, as this requires reevaluating the energy at each of
886 the constraint components. This functionality is planned for later
891 ; Include force-field parameters
892 #include "gromos43a1.ff/forcefield.itp"
899 ; nr type resnr residu atom cgnr charge mass
900 1 CH4 1 CH4 C1 1 0 16.043
901 2 CH4 1 CH4 C2 2 0 16.043
903 ; ai aj funct length_A length_B
906 #include "gromos43a1.ff/spc.itp"
920 Files with the :ref:`gro` file extension contain a molecular
921 structure in GROMOS-87 format. A sample piece is included below:
925 MD of 2 waters, reformat step, PA aug-91
927 1WATER OW1 1 0.126 1.624 1.679 0.1227 -0.0580 0.0434
928 1WATER HW2 2 0.190 1.661 1.747 0.8085 0.3191 -0.7791
929 1WATER HW3 3 0.177 1.568 1.613 -0.9045 -2.6469 1.3180
930 2WATER OW1 4 1.275 0.053 0.622 0.2519 0.3140 -0.1734
931 2WATER HW2 5 1.337 0.002 0.680 -1.0641 -1.1349 0.0257
932 2WATER HW3 6 1.326 0.120 0.568 1.9427 -0.8216 -0.0244
933 1.82060 1.82060 1.82060
935 This format is fixed, *i.e.* all columns are in a fixed position. If you
936 want to read such a file in your own program without using the |Gromacs|
937 libraries you can use the following formats:
940 ``“%5i%5s%5s%5i%8.3f%8.3f%8.3f%8.4f%8.4f%8.4f”``
942 Or to be more precise, with title *etc.* it looks like this:
948 for (i=0; (i<natoms); i++) {
949 "%5d%-5s%5s%5d%8.3f%8.3f%8.3f%8.4f%8.4f%8.4f\n",
950 residuenr,residuename,atomname,atomnr,x,y,z,vx,vy,vz
952 "%10.5f%10.5f%10.5f%10.5f%10.5f%10.5f%10.5f%10.5f%10.5f\n",
953 box[X][X],box[Y][Y],box[Z][Z],
954 box[X][Y],box[X][Z],box[Y][X],box[Y][Z],box[Z][X],box[Z][Y]
957 ``(i5,2a5,i5,3f8.3,3f8.4)``
959 So ``confin.gro`` is the |Gromacs| coordinate file and is
960 almost the same as the GROMOS-87 file (for GROMOS users: when used with
961 ``ntx=7``). The only difference is the box for which |Gromacs|
962 uses a tensor, not a vector.