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38 * This file contains function definitions necessary
39 * for computations of forces due to restricted angle, restricted dihedral and
40 * combined bending-torsion potentials.
42 * \author Nicolae Goga
44 * \ingroup module_listed_forces
52 #include "gromacs/math/functions.h"
53 #include "gromacs/math/units.h"
54 #include "gromacs/math/utilities.h"
55 #include "gromacs/math/vec.h"
56 #include "gromacs/topology/idef.h"
58 /* This function computes factors needed for restricted angle potential.
59 * For explanations on formula used see file "restcbt.h" */
61 void compute_factors_restangles(int type, const t_iparams forceparams[],
62 rvec delta_ante, rvec delta_post,
63 double *prefactor, double *ratio_ante, double *ratio_post, real *v)
65 // These variables are double to make the code
67 double theta_equil, k_bending;
68 double cosine_theta_equil;
69 double c_ante, c_cros, c_post;
71 double delta_cosine, cosine_theta;
73 double term_theta_theta_equil;
75 k_bending = forceparams[type].harmonic.krA;
76 theta_equil = forceparams[type].harmonic.rA*DEG2RAD;
77 theta_equil = M_PI - theta_equil;
78 cosine_theta_equil = cos(theta_equil);
80 c_ante = iprod(delta_ante, delta_ante);
81 c_cros = iprod(delta_ante, delta_post);
82 c_post = iprod(delta_post, delta_post);
84 norm = gmx::invsqrt(c_ante * c_post);
85 cosine_theta = c_cros * norm;
86 sine_theta_sq = 1 - cosine_theta * cosine_theta;
88 *ratio_ante = c_cros / c_ante;
89 *ratio_post = c_cros / c_post;
91 delta_cosine = cosine_theta - cosine_theta_equil;
92 term_theta_theta_equil = 1 - cosine_theta * cosine_theta_equil;
93 *prefactor = -(k_bending) * delta_cosine * norm * term_theta_theta_equil / (sine_theta_sq * sine_theta_sq);
95 *v = k_bending * 0.5 * delta_cosine * delta_cosine / sine_theta_sq;
100 /* Compute factors for restricted dihedral potential
101 * For explanations on formula used see file "restcbt.h" */
102 void compute_factors_restrdihs(int type, const t_iparams forceparams[],
103 rvec delta_ante, rvec delta_crnt, rvec delta_post,
104 real *factor_phi_ai_ante, real *factor_phi_ai_crnt, real *factor_phi_ai_post,
105 real *factor_phi_aj_ante, real *factor_phi_aj_crnt, real *factor_phi_aj_post,
106 real *factor_phi_ak_ante, real *factor_phi_ak_crnt, real *factor_phi_ak_post,
107 real *factor_phi_al_ante, real *factor_phi_al_crnt, real *factor_phi_al_post,
108 real *prefactor_phi, real *v)
111 real phi0, cosine_phi0;
113 real c_self_ante, c_self_crnt, c_self_post;
114 real c_cros_ante, c_cros_acrs, c_cros_post;
115 real c_prod, d_post, d_ante;
116 real sine_phi_sq, cosine_phi;
117 real delta_cosine, term_phi_phi0;
118 real ratio_phi_ante, ratio_phi_post;
121 /* Read parameters phi0 and k_torsion */
122 phi0 = forceparams[type].pdihs.phiA * DEG2RAD;
123 cosine_phi0 = cos(phi0);
124 k_torsion = forceparams[type].pdihs.cpA;
126 /* Computation of the cosine of the dihedral angle. The scalar ("dot") product method
127 * is used. c_*_* cummulate the scalar products of the differences of particles
128 * positions while c_prod, d_ante and d_post are differences of products of scalar
129 * terms that are parts of the derivatives of forces */
130 c_self_ante = iprod(delta_ante, delta_ante);
131 c_self_crnt = iprod(delta_crnt, delta_crnt);
132 c_self_post = iprod(delta_post, delta_post);
133 c_cros_ante = iprod(delta_ante, delta_crnt);
134 c_cros_acrs = iprod(delta_ante, delta_post);
135 c_cros_post = iprod(delta_crnt, delta_post);
136 c_prod = c_cros_ante * c_cros_post - c_self_crnt * c_cros_acrs;
137 d_ante = c_self_ante * c_self_crnt - c_cros_ante * c_cros_ante;
138 d_post = c_self_post * c_self_crnt - c_cros_post * c_cros_post;
140 /* When three consecutive beads align, we obtain values close to zero.
141 * Here we avoid small values to prevent round-off errors. */
142 if (d_ante < GMX_REAL_EPS)
144 d_ante = GMX_REAL_EPS;
146 if (d_post < GMX_REAL_EPS)
148 d_post = GMX_REAL_EPS;
151 /* Computes the square of the sinus of phi in sine_phi_sq */
152 norm_phi = gmx::invsqrt(d_ante * d_post);
153 cosine_phi = c_prod * norm_phi;
154 sine_phi_sq = 1.0 - cosine_phi * cosine_phi;
156 /* It is possible that cosine_phi is slightly bigger than 1.0 due to round-off errors. */
157 if (sine_phi_sq < 0.0)
162 /* Computation of the differences of cosines (delta_cosine) and a term (term_phi_phi0)
163 * that is part of the common prefactor_phi */
165 delta_cosine = cosine_phi - cosine_phi0;
166 term_phi_phi0 = 1 - cosine_phi * cosine_phi0;
169 /* Computation of ratios */
170 ratio_phi_ante = c_prod / d_ante;
171 ratio_phi_post = c_prod / d_post;
173 /* Computation of the prefactor - common term for all forces */
174 *prefactor_phi = -(k_torsion) * delta_cosine * norm_phi * term_phi_phi0 / (sine_phi_sq * sine_phi_sq);
176 /* Computation of force factors. Factors factor_phi_* are coming from the
177 * derivatives of the torsion angle (phi) with respect to the beads ai, aj, al, ak,
178 * (four) coordinates and they are multiplied in the force computations with the
179 * differences of the particles positions stored in parameters delta_ante,
180 * delta_crnt, delta_post. For formulas see file "restcbt.h" */
182 *factor_phi_ai_ante = ratio_phi_ante * c_self_crnt;
183 *factor_phi_ai_crnt = -c_cros_post - ratio_phi_ante * c_cros_ante;
184 *factor_phi_ai_post = c_self_crnt;
185 *factor_phi_aj_ante = -c_cros_post - ratio_phi_ante * (c_self_crnt + c_cros_ante);
186 *factor_phi_aj_crnt = c_cros_post + c_cros_acrs * 2.0 + ratio_phi_ante * (c_self_ante + c_cros_ante) + ratio_phi_post * c_self_post;
187 *factor_phi_aj_post = -(c_cros_ante + c_self_crnt) - ratio_phi_post * c_cros_post;
188 *factor_phi_ak_ante = c_cros_post + c_self_crnt + ratio_phi_ante * c_cros_ante;
189 *factor_phi_ak_crnt = -(c_cros_ante + c_cros_acrs * 2.0)- ratio_phi_ante * c_self_ante - ratio_phi_post * (c_self_post + c_cros_post);
190 *factor_phi_ak_post = c_cros_ante + ratio_phi_post * (c_self_crnt + c_cros_post);
191 *factor_phi_al_ante = -c_self_crnt;
192 *factor_phi_al_crnt = c_cros_ante + ratio_phi_post * c_cros_post;
193 *factor_phi_al_post = -ratio_phi_post * c_self_crnt;
195 /* Contribution to energy - see formula in file "restcbt.h"*/
196 *v = k_torsion * 0.5 * delta_cosine * delta_cosine / sine_phi_sq;
201 /* Compute factors for CBT potential
202 * For explanations on formula used see file "restcbt.h" */
204 void compute_factors_cbtdihs(int type, const t_iparams forceparams[],
205 rvec delta_ante, rvec delta_crnt, rvec delta_post,
206 rvec f_phi_ai, rvec f_phi_aj, rvec f_phi_ak, rvec f_phi_al,
207 rvec f_theta_ante_ai, rvec f_theta_ante_aj, rvec f_theta_ante_ak,
208 rvec f_theta_post_aj, rvec f_theta_post_ak, rvec f_theta_post_al,
212 real torsion_coef[NR_CBTDIHS];
213 real c_self_ante, c_self_crnt, c_self_post;
214 real c_cros_ante, c_cros_acrs, c_cros_post;
215 real c_prod, d_ante, d_post;
216 real norm_phi, norm_theta_ante, norm_theta_post;
217 real cosine_phi, cosine_theta_ante, cosine_theta_post;
218 real sine_theta_ante_sq, sine_theta_post_sq;
219 real sine_theta_ante, sine_theta_post;
221 real ratio_phi_ante, ratio_phi_post;
223 real factor_phi_ai_ante, factor_phi_ai_crnt, factor_phi_ai_post;
224 real factor_phi_aj_ante, factor_phi_aj_crnt, factor_phi_aj_post;
225 real factor_phi_ak_ante, factor_phi_ak_crnt, factor_phi_ak_post;
226 real factor_phi_al_ante, factor_phi_al_crnt, factor_phi_al_post;
227 real prefactor_theta_ante, ratio_theta_ante_ante, ratio_theta_ante_crnt;
228 real prefactor_theta_post, ratio_theta_post_crnt, ratio_theta_post_post;
230 /* The formula for combined bending-torsion potential (see file "restcbt.h") contains
231 * in its expression not only the dihedral angle \f[\phi\f] but also \f[\theta_{i-1}\f]
232 * (theta_ante bellow) and \f[\theta_{i}\f] (theta_post bellow)--- the adjacent bending
233 * angles. The forces for the particles ai, aj, ak, al have components coming from the
234 * derivatives of the potential with respect to all three angles.
235 * This function is organised in 4 parts
236 * PART 1 - Computes force factors common to all the derivatives for the four particles
237 * PART 2 - Computes the force components due to the derivatives of dihedral angle Phi
238 * PART 3 - Computes the force components due to the derivatives of bending angle Theta_Ante
239 * PART 4 - Computes the force components due to the derivatives of bending angle Theta_Post
240 * Bellow we will respct thuis structure */
243 /* PART 1 - COMPUTES FORCE FACTORS COMMON TO ALL DERIVATIVES FOR THE FOUR PARTICLES */
246 for (j = 0; (j < NR_CBTDIHS); j++)
248 torsion_coef[j] = forceparams[type].cbtdihs.cbtcA[j];
251 /* Computation of the cosine of the dihedral angle. The scalar ("dot") product method
252 * is used. c_*_* cummulate the scalar products of the differences of particles
253 * positions while c_prod, d_ante and d_post are differences of products of scalar
254 * terms that are parts of the derivatives of forces */
256 c_self_ante = iprod(delta_ante, delta_ante);
257 c_self_crnt = iprod(delta_crnt, delta_crnt);
258 c_self_post = iprod(delta_post, delta_post);
259 c_cros_ante = iprod(delta_ante, delta_crnt);
260 c_cros_acrs = iprod(delta_ante, delta_post);
261 c_cros_post = iprod(delta_crnt, delta_post);
262 c_prod = c_cros_ante * c_cros_post - c_self_crnt * c_cros_acrs;
263 d_ante = c_self_ante * c_self_crnt - c_cros_ante * c_cros_ante;
264 d_post = c_self_post * c_self_crnt - c_cros_post * c_cros_post;
266 /* When three consecutive beads align, we obtain values close to zero.
267 Here we avoid small values to prevent round-off errors. */
268 if (d_ante < GMX_REAL_EPS)
270 d_ante = GMX_REAL_EPS;
272 if (d_post < GMX_REAL_EPS)
274 d_post = GMX_REAL_EPS;
277 /* Computations of cosines */
278 norm_phi = gmx::invsqrt(d_ante * d_post);
279 norm_theta_ante = gmx::invsqrt(c_self_ante * c_self_crnt);
280 norm_theta_post = gmx::invsqrt(c_self_crnt * c_self_post);
281 cosine_phi = c_prod * norm_phi;
282 cosine_theta_ante = c_cros_ante * norm_theta_ante;
283 cosine_theta_post = c_cros_post * norm_theta_post;
284 sine_theta_ante_sq = 1 - cosine_theta_ante * cosine_theta_ante;
285 sine_theta_post_sq = 1 - cosine_theta_post * cosine_theta_post;
287 /* It is possible that cosine_theta is slightly bigger than 1.0 due to round-off errors. */
288 if (sine_theta_ante_sq < 0.0)
290 sine_theta_ante_sq = 0.0;
292 if (sine_theta_post_sq < 0.0)
294 sine_theta_post_sq = 0.0;
297 sine_theta_ante = std::sqrt(sine_theta_ante_sq);
298 sine_theta_post = std::sqrt(sine_theta_post_sq);
300 /* PART 2 - COMPUTES FORCE COMPONENTS DUE TO DERIVATIVES TO DIHEDRAL ANGLE PHI */
302 /* Computation of ratios */
303 ratio_phi_ante = c_prod / d_ante;
304 ratio_phi_post = c_prod / d_post;
306 /* Computation of the prefactor */
307 /* Computing 2nd power */
310 prefactor_phi = -torsion_coef[0] * norm_phi * (torsion_coef[2] + torsion_coef[3] * 2.0 * cosine_phi + torsion_coef[4] * 3.0 * (r1 * r1) + 4*torsion_coef[5]*r1*r1*r1) *
311 sine_theta_ante_sq * sine_theta_ante * sine_theta_post_sq * sine_theta_post;
313 /* Computation of factors (important for gaining speed). Factors factor_phi_* are coming from the
314 * derivatives of the torsion angle (phi) with respect to the beads ai, aj, al, ak,
315 * (four) coordinates and they are multiplied in the force computations with the
316 * differences of the particles positions stored in parameters delta_ante,
317 * delta_crnt, delta_post. For formulas see file "restcbt.h" */
319 factor_phi_ai_ante = ratio_phi_ante * c_self_crnt;
320 factor_phi_ai_crnt = -c_cros_post - ratio_phi_ante * c_cros_ante;
321 factor_phi_ai_post = c_self_crnt;
322 factor_phi_aj_ante = -c_cros_post - ratio_phi_ante * (c_self_crnt + c_cros_ante);
323 factor_phi_aj_crnt = c_cros_post + c_cros_acrs * 2.0 + ratio_phi_ante * (c_self_ante + c_cros_ante) + ratio_phi_post * c_self_post;
324 factor_phi_aj_post = -(c_cros_ante + c_self_crnt) - ratio_phi_post * c_cros_post;
325 factor_phi_ak_ante = c_cros_post + c_self_crnt + ratio_phi_ante * c_cros_ante;
326 factor_phi_ak_crnt = -(c_cros_ante + c_cros_acrs * 2.0) - ratio_phi_ante * c_self_ante - ratio_phi_post * (c_self_post + c_cros_post);
327 factor_phi_ak_post = c_cros_ante + ratio_phi_post * (c_self_crnt + c_cros_post);
328 factor_phi_al_ante = -c_self_crnt;
329 factor_phi_al_crnt = c_cros_ante + ratio_phi_post * c_cros_post;
330 factor_phi_al_post = -ratio_phi_post * c_self_crnt;
332 /* Computation of forces due to the derivatives of dihedral angle phi*/
333 for (d = 0; d < DIM; d++)
335 f_phi_ai[d] = prefactor_phi * (factor_phi_ai_ante * delta_ante[d] + factor_phi_ai_crnt * delta_crnt[d] + factor_phi_ai_post * delta_post[d]);
336 f_phi_aj[d] = prefactor_phi * (factor_phi_aj_ante * delta_ante[d] + factor_phi_aj_crnt * delta_crnt[d] + factor_phi_aj_post * delta_post[d]);
337 f_phi_ak[d] = prefactor_phi * (factor_phi_ak_ante * delta_ante[d] + factor_phi_ak_crnt * delta_crnt[d] + factor_phi_ak_post * delta_post[d]);
338 f_phi_al[d] = prefactor_phi * (factor_phi_al_ante * delta_ante[d] + factor_phi_al_crnt * delta_crnt[d] + factor_phi_al_post * delta_post[d]);
341 /* PART 3 - COMPUTES THE FORCE COMPONENTS DUE TO THE DERIVATIVES OF BENDING ANGLE THETHA_ANTHE */
342 /* Computation of ratios */
343 ratio_theta_ante_ante = c_cros_ante / c_self_ante;
344 ratio_theta_ante_crnt = c_cros_ante / c_self_crnt;
346 /* Computation of the prefactor */
347 /* Computing 2nd power */
349 /* Computing 3rd power */
352 prefactor_theta_ante = -torsion_coef[0] * norm_theta_ante * ( torsion_coef[1] + torsion_coef[2] * cosine_phi + torsion_coef[3] * (r1 * r1) +
353 torsion_coef[4] * (r2 * (r2 * r2))+ torsion_coef[5] * (r2 * (r2 * (r2 * r2)))) * (-3.0) * cosine_theta_ante * sine_theta_ante * sine_theta_post_sq * sine_theta_post;
356 /* Computation of forces due to the derivatives of bending angle theta_ante */
357 for (d = 0; d < DIM; d++)
359 f_theta_ante_ai[d] = prefactor_theta_ante * (ratio_theta_ante_ante * delta_ante[d] - delta_crnt[d]);
360 f_theta_ante_aj[d] = prefactor_theta_ante * ((ratio_theta_ante_crnt + 1.0) * delta_crnt[d] - (ratio_theta_ante_ante + 1.0) * delta_ante[d]);
361 f_theta_ante_ak[d] = prefactor_theta_ante * (delta_ante[d] - ratio_theta_ante_crnt * delta_crnt[d]);
364 /* PART 4 - COMPUTES THE FORCE COMPONENTS DUE TO THE DERIVATIVES OF THE BENDING ANGLE THETA_POST */
366 /* Computation of ratios */
367 ratio_theta_post_crnt = c_cros_post / c_self_crnt;
368 ratio_theta_post_post = c_cros_post / c_self_post;
370 /* Computation of the prefactor */
371 /* Computing 2nd power */
373 /* Computing 3rd power */
376 prefactor_theta_post = -torsion_coef[0] * norm_theta_post * (torsion_coef[1] + torsion_coef[2] * cosine_phi + torsion_coef[3] * (r1 * r1) +
377 torsion_coef[4] * (r2 * (r2 * r2)) + torsion_coef[5] * (r2 * (r2 * (r2 * r2)))) * sine_theta_ante_sq * sine_theta_ante * (-3.0) * cosine_theta_post * sine_theta_post;
380 /* Computation of forces due to the derivatives of bending angle Theta_Post */
381 for (d = 0; d < DIM; d++)
383 f_theta_post_aj[d] = prefactor_theta_post * (ratio_theta_post_crnt * delta_crnt[d] - delta_post[d]);
384 f_theta_post_ak[d] = prefactor_theta_post * ((ratio_theta_post_post + 1.0) * delta_post[d] - (ratio_theta_post_crnt + 1.0) * delta_crnt[d]);
385 f_theta_post_al[d] = prefactor_theta_post * (delta_crnt[d] - ratio_theta_post_post * delta_post[d]);
390 /* Contribution to energy - for formula see file "restcbt.h" */
391 *v = torsion_coef[0] * (torsion_coef[1] + torsion_coef[2] * cosine_phi + torsion_coef[3] * (r1 * r1) +
392 torsion_coef[4] * (r2 * (r2 * r2)) + torsion_coef[5] * (r2 * (r2 * (r2 * r2)))) * sine_theta_ante_sq *
393 sine_theta_ante * sine_theta_post_sq * sine_theta_post;