2 * This file is part of the GROMACS molecular simulation package.
4 * Copyright (c) 2012,2013,2014,2015,2016 by the GROMACS development team.
5 * Copyright (c) 2018,2019,2020, by the GROMACS development team, led by
6 * Mark Abraham, David van der Spoel, Berk Hess, and Erik Lindahl,
7 * and including many others, as listed in the AUTHORS file in the
8 * top-level source directory and at http://www.gromacs.org.
10 * GROMACS is free software; you can redistribute it and/or
11 * modify it under the terms of the GNU Lesser General Public License
12 * as published by the Free Software Foundation; either version 2.1
13 * of the License, or (at your option) any later version.
15 * GROMACS is distributed in the hope that it will be useful,
16 * but WITHOUT ANY WARRANTY; without even the implied warranty of
17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18 * Lesser General Public License for more details.
20 * You should have received a copy of the GNU Lesser General Public
21 * License along with GROMACS; if not, see
22 * http://www.gnu.org/licenses, or write to the Free Software Foundation,
23 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
25 * If you want to redistribute modifications to GROMACS, please
26 * consider that scientific software is very special. Version
27 * control is crucial - bugs must be traceable. We will be happy to
28 * consider code for inclusion in the official distribution, but
29 * derived work must not be called official GROMACS. Details are found
30 * in the README & COPYING files - if they are missing, get the
31 * official version at http://www.gromacs.org.
33 * To help us fund GROMACS development, we humbly ask that you cite
34 * the research papers on the package. Check out http://www.gromacs.org.
37 /* When calculating RF or Ewald interactions we calculate the electrostatic
38 * forces and energies on excluded atom pairs here in the non-bonded loops.
40 #if defined CHECK_EXCLS && (defined CALC_COULOMB || defined LJ_EWALD)
54 egp_cj = nbatParams.energrp[cj];
56 for (i = 0; i < UNROLLI; i++)
62 ai = ci * UNROLLI + i;
64 type_i_off = type[ai] * ntype2;
66 for (j = 0; j < UNROLLJ; j++)
73 real FrLJ6 = 0, FrLJ12 = 0, frLJ = 0;
75 #if defined LJ_FORCE_SWITCH || defined LJ_POT_SWITCH
94 /* A multiply mask used to zero an interaction
95 * when either the distance cutoff is exceeded, or
96 * (if appropriate) the i and j indices are
97 * unsuitable for this kind of inner loop. */
101 /* A multiply mask used to zero an interaction
102 * when that interaction should be excluded
103 * (e.g. because of bonding). */
104 real interact = static_cast<real>((l_cj[cjind].excl >> (i * UNROLLI + j)) & 1);
108 skipmask = (cj == ci_sh && j <= i) ? 0.0 : 1.0;
111 constexpr real interact = 1.0;
117 aj = cj * UNROLLJ + j;
119 dx = xi[i * XI_STRIDE + XX] - x[aj * X_STRIDE + XX];
120 dy = xi[i * XI_STRIDE + YY] - x[aj * X_STRIDE + YY];
121 dz = xi[i * XI_STRIDE + ZZ] - x[aj * X_STRIDE + ZZ];
123 rsq = dx * dx + dy * dy + dz * dz;
125 /* Prepare to enforce the cut-off. */
126 skipmask = (rsq >= rcut2) ? 0 : skipmask;
127 /* 9 flops for r^2 + cut-off check */
129 // Ensure the distances do not fall below the limit where r^-12 overflows.
130 // This should never happen for normal interactions.
131 rsq = std::max(rsq, c_nbnxnMinDistanceSquared);
137 rinv = gmx::invsqrt(rsq);
138 /* 5 flops for invsqrt */
140 /* Partially enforce the cut-off (and perhaps
141 * exclusions) to avoid possible overflow of
142 * rinvsix when computing LJ, and/or overflowing
143 * the Coulomb table during lookup. */
144 rinv = rinv * skipmask;
146 rinvsq = rinv * rinv;
152 c6 = nbfp[type_i_off + type[aj] * 2];
153 c12 = nbfp[type_i_off + type[aj] * 2 + 1];
155 #if defined LJ_CUT || defined LJ_FORCE_SWITCH || defined LJ_POT_SWITCH
156 rinvsix = interact * rinvsq * rinvsq * rinvsq;
157 FrLJ6 = c6 * rinvsix;
158 FrLJ12 = c12 * rinvsix * rinvsix;
159 frLJ = FrLJ12 - FrLJ6;
160 /* 7 flops for r^-2 + LJ force */
161 # if defined CALC_ENERGIES || defined LJ_POT_SWITCH
162 VLJ = (FrLJ12 + c12 * ic->repulsion_shift.cpot) / 12
163 - (FrLJ6 + c6 * ic->dispersion_shift.cpot) / 6;
164 /* 7 flops for LJ energy */
168 #if defined LJ_FORCE_SWITCH || defined LJ_POT_SWITCH
169 /* Force or potential switching from ic->rvdw_switch */
171 rsw = r - ic->rvdw_switch;
172 rsw = (rsw >= 0.0 ? rsw : 0.0);
174 #ifdef LJ_FORCE_SWITCH
175 frLJ += -c6 * (ic->dispersion_shift.c2 + ic->dispersion_shift.c3 * rsw) * rsw * rsw * r
176 + c12 * (ic->repulsion_shift.c2 + ic->repulsion_shift.c3 * rsw) * rsw * rsw * r;
177 # if defined CALC_ENERGIES
178 VLJ += -c6 * (-ic->dispersion_shift.c2 / 3 - ic->dispersion_shift.c3 / 4 * rsw)
180 + c12 * (-ic->repulsion_shift.c2 / 3 - ic->repulsion_shift.c3 / 4 * rsw)
185 #if defined CALC_ENERGIES || defined LJ_POT_SWITCH
186 /* Masking should be done after force switching,
187 * but before potential switching.
189 /* Need to zero the interaction if there should be exclusion. */
190 VLJ = VLJ * interact;
197 sw = 1.0 + (swV3 + (swV4 + swV5 * rsw) * rsw) * rsw * rsw * rsw;
198 dsw = (swF2 + (swF3 + swF4 * rsw) * rsw) * rsw * rsw;
200 frLJ = frLJ * sw - r * VLJ * dsw;
207 real c6grid, rinvsix_nm, cr2, expmcr2, poly;
208 # ifdef CALC_ENERGIES
212 # ifdef LJ_EWALD_COMB_GEOM
213 c6grid = ljc[type[ai] * 2] * ljc[type[aj] * 2];
214 # elif defined LJ_EWALD_COMB_LB
216 real sigma, sigma2, epsilon;
218 /* These sigma and epsilon are scaled to give 6*C6 */
219 sigma = ljc[type[ai] * 2] + ljc[type[aj] * 2];
220 epsilon = ljc[type[ai] * 2 + 1] * ljc[type[aj] * 2 + 1];
222 sigma2 = sigma * sigma;
223 c6grid = epsilon * sigma2 * sigma2 * sigma2;
226 # error "No LJ Ewald combination rule defined"
230 /* Recalculate rinvsix without exclusion mask */
231 rinvsix_nm = rinvsq * rinvsq * rinvsq;
233 rinvsix_nm = rinvsix;
235 cr2 = lje_coeff2 * rsq;
239 expmcr2 = expf(-cr2);
241 poly = 1 + cr2 + 0.5 * cr2 * cr2;
243 /* Subtract the grid force from the total LJ force */
244 frLJ += c6grid * (rinvsix_nm - expmcr2 * (rinvsix_nm * poly + lje_coeff6_6));
245 # ifdef CALC_ENERGIES
246 /* Shift should only be applied to real LJ pairs */
247 sh_mask = lje_vc * interact;
249 VLJ += c6grid / 6 * (rinvsix_nm * (1 - expmcr2 * poly) + sh_mask);
252 #endif /* LJ_EWALD */
254 #ifdef VDW_CUTOFF_CHECK
255 /* Mask for VdW cut-off shorter than Coulomb cut-off */
259 skipmask_rvdw = (rsq < rvdw2) ? 1.0 : 0.0;
260 frLJ *= skipmask_rvdw;
261 # ifdef CALC_ENERGIES
262 VLJ *= skipmask_rvdw;
266 # if defined CALC_ENERGIES
267 /* Need to zero the interaction if r >= rcut */
268 VLJ = VLJ * skipmask;
269 /* 1 more flop for LJ energy */
271 #endif /* VDW_CUTOFF_CHECK */
275 # ifdef ENERGY_GROUPS
276 Vvdw[egp_sh_i[i] + ((egp_cj >> (nbatParams.neg_2log * j)) & egp_mask)] += VLJ;
279 /* 1 flop for LJ energy addition */
285 /* Enforce the cut-off and perhaps exclusions. In
286 * those cases, rinv is zero because of skipmask,
287 * but fcoul and vcoul will later be non-zero (in
288 * both RF and table cases) because of the
289 * contributions that do not depend on rinv. These
290 * contributions cannot be allowed to accumulate
291 * to the force and potential, and the easiest way
292 * to do this is to zero the charges in
294 qq = skipmask * qi[i] * q[aj];
297 fcoul = qq * (interact * rinv * rinvsq - k_rf2);
298 /* 4 flops for RF force */
299 # ifdef CALC_ENERGIES
300 vcoul = qq * (interact * rinv + k_rf * rsq - c_rf);
301 /* 4 flops for RF energy */
305 # ifdef CALC_COUL_TAB
306 rs = rsq * rinv * tab_coul_scale;
308 frac = rs - static_cast<real>(ri);
310 /* fexcl = F_i + frac * (F_(i+1)-F_i) */
311 fexcl = tab_coul_FDV0[ri * 4] + frac * tab_coul_FDV0[ri * 4 + 1];
313 /* fexcl = (1-frac) * F_i + frac * F_(i+1) */
314 fexcl = (1 - frac) * tab_coul_F[ri] + frac * tab_coul_F[ri + 1];
316 fcoul = interact * rinvsq - fexcl;
317 /* 7 flops for float 1/r-table force */
318 # ifdef CALC_ENERGIES
321 * (interact * (rinv - ic->sh_ewald)
322 - (tab_coul_FDV0[ri * 4 + 2] - halfsp * frac * (tab_coul_FDV0[ri * 4] + fexcl)));
323 /* 7 flops for float 1/r-table energy (8 with excls) */
326 * (interact * (rinv - ic->sh_ewald)
327 - (tab_coul_V[ri] - halfsp * frac * (tab_coul_F[ri] + fexcl)));
333 # ifdef CALC_ENERGIES
334 # ifdef ENERGY_GROUPS
335 Vc[egp_sh_i[i] + ((egp_cj >> (nbatParams.neg_2log * j)) & egp_mask)] += vcoul;
338 /* 1 flop for Coulomb energy addition */
348 fscal = frLJ * rinvsq + fcoul;
349 /* 2 flops for scalar LJ+Coulomb force */
358 fscal = frLJ * rinvsq;
364 /* Increment i-atom force */
365 fi[i * FI_STRIDE + XX] += fx;
366 fi[i * FI_STRIDE + YY] += fy;
367 fi[i * FI_STRIDE + ZZ] += fz;
368 /* Decrement j-atom force */
369 f[aj * F_STRIDE + XX] -= fx;
370 f[aj * F_STRIDE + YY] -= fy;
371 f[aj * F_STRIDE + ZZ] -= fz;
372 /* 9 flops for force addition */