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36 /* When calculating RF or Ewald interactions we calculate the electrostatic
37 * forces and energies on excluded atom pairs here in the non-bonded loops.
39 #if defined CHECK_EXCLS && defined CALC_COULOMB
53 egp_cj = nbat->energrp[cj];
55 for (i = 0; i < UNROLLI; i++)
63 type_i_off = type[ai]*ntype2;
65 for (j = 0; j < UNROLLJ; j++)
72 real FrLJ6 = 0, FrLJ12 = 0, frLJ = 0, VLJ = 0;
73 #if defined VDW_FORCE_SWITCH || defined VDW_POT_SWITCH
92 /* A multiply mask used to zero an interaction
93 * when either the distance cutoff is exceeded, or
94 * (if appropriate) the i and j indices are
95 * unsuitable for this kind of inner loop. */
99 /* A multiply mask used to zero an interaction
100 * when that interaction should be excluded
101 * (e.g. because of bonding). */
104 interact = ((l_cj[cjind].excl>>(i*UNROLLI + j)) & 1);
108 skipmask = !(cj == ci_sh && j <= i);
117 dx = xi[i*XI_STRIDE+XX] - x[aj*X_STRIDE+XX];
118 dy = xi[i*XI_STRIDE+YY] - x[aj*X_STRIDE+YY];
119 dz = xi[i*XI_STRIDE+ZZ] - x[aj*X_STRIDE+ZZ];
121 rsq = dx*dx + dy*dy + dz*dz;
123 /* Prepare to enforce the cut-off. */
124 skipmask = (rsq >= rcut2) ? 0 : skipmask;
125 /* 9 flops for r^2 + cut-off check */
128 /* Excluded atoms are allowed to be on top of each other.
129 * To avoid overflow of rinv, rinvsq and rinvsix
130 * we add a small number to rsq for excluded pairs only.
132 rsq += (1 - interact)*NBNXN_AVOID_SING_R2_INC;
139 rinv = gmx_invsqrt(rsq);
140 /* 5 flops for invsqrt */
142 /* Partially enforce the cut-off (and perhaps
143 * exclusions) to avoid possible overflow of
144 * rinvsix when computing LJ, and/or overflowing
145 * the Coulomb table during lookup. */
146 rinv = rinv * skipmask;
154 rinvsix = interact*rinvsq*rinvsq*rinvsq;
156 c6 = nbfp[type_i_off+type[aj]*2 ];
157 c12 = nbfp[type_i_off+type[aj]*2+1];
159 FrLJ12 = c12*rinvsix*rinvsix;
160 frLJ = FrLJ12 - FrLJ6;
161 /* 7 flops for r^-2 + LJ force */
162 #if defined CALC_ENERGIES || defined VDW_POT_SWITCH
163 VLJ = (FrLJ12 + c12*ic->repulsion_shift.cpot)/12 -
164 (FrLJ6 + c6*ic->dispersion_shift.cpot)/6;
165 /* 7 flops for LJ energy */
168 #if defined VDW_FORCE_SWITCH || defined VDW_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 VDW_FORCE_SWITCH
176 -c6*(ic->dispersion_shift.c2 + ic->dispersion_shift.c3*rsw)*rsw*rsw*r
177 + c12*(ic->repulsion_shift.c2 + ic->repulsion_shift.c3*rsw)*rsw*rsw*r;
178 #if defined CALC_ENERGIES
180 -c6*(-ic->dispersion_shift.c2/3 - ic->dispersion_shift.c3/4*rsw)*rsw*rsw*rsw
181 + c12*(-ic->repulsion_shift.c2/3 - ic->repulsion_shift.c3/4*rsw)*rsw*rsw*rsw;
185 #if defined CALC_ENERGIES || defined VDW_POT_SWITCH
186 /* Masking shoule be done after force switching,
187 * but before potential switching.
189 /* Need to zero the interaction if r >= rcut
190 * or there should be exclusion. */
191 VLJ = VLJ * skipmask * interact;
192 /* 2 more flops for LJ energy */
195 #ifdef VDW_POT_SWITCH
199 sw = 1.0 + (swV3 + (swV4+ swV5*rsw)*rsw)*rsw*rsw*rsw;
200 dsw = (swF2 + (swF3 + swF4*rsw)*rsw)*rsw*rsw;
202 frLJ = frLJ*sw - r*VLJ*dsw;
207 #ifdef VDW_CUTOFF_CHECK
208 /* Mask for VdW cut-off shorter than Coulomb cut-off */
212 skipmask_rvdw = (rsq < rvdw2);
213 frLJ *= skipmask_rvdw;
215 VLJ *= skipmask_rvdw;
222 Vvdw[egp_sh_i[i]+((egp_cj>>(nbat->neg_2log*j)) & egp_mask)] += VLJ;
225 /* 1 flop for LJ energy addition */
231 /* Enforce the cut-off and perhaps exclusions. In
232 * those cases, rinv is zero because of skipmask,
233 * but fcoul and vcoul will later be non-zero (in
234 * both RF and table cases) because of the
235 * contributions that do not depend on rinv. These
236 * contributions cannot be allowed to accumulate
237 * to the force and potential, and the easiest way
238 * to do this is to zero the charges in
240 qq = skipmask * qi[i] * q[aj];
243 fcoul = qq*(interact*rinv*rinvsq - k_rf2);
244 /* 4 flops for RF force */
246 vcoul = qq*(interact*rinv + k_rf*rsq - c_rf);
247 /* 4 flops for RF energy */
252 rs = rsq*rinv*ic->tabq_scale;
256 /* fexcl = F_i + frac * (F_(i+1)-F_i) */
257 fexcl = tab_coul_FDV0[ri*4] + frac*tab_coul_FDV0[ri*4+1];
259 /* fexcl = (1-frac) * F_i + frac * F_(i+1) */
260 fexcl = (1 - frac)*tab_coul_F[ri] + frac*tab_coul_F[ri+1];
262 fcoul = interact*rinvsq - fexcl;
263 /* 7 flops for float 1/r-table force */
266 vcoul = qq*(interact*(rinv - ic->sh_ewald)
267 -(tab_coul_FDV0[ri*4+2]
268 -halfsp*frac*(tab_coul_FDV0[ri*4] + fexcl)));
269 /* 7 flops for float 1/r-table energy (8 with excls) */
271 vcoul = qq*(interact*(rinv - ic->sh_ewald)
273 -halfsp*frac*(tab_coul_F[ri] + fexcl)));
281 Vc[egp_sh_i[i]+((egp_cj>>(nbat->neg_2log*j)) & egp_mask)] += vcoul;
284 /* 1 flop for Coulomb energy addition */
294 fscal = frLJ*rinvsq + fcoul;
295 /* 2 flops for scalar LJ+Coulomb force */
310 /* Increment i-atom force */
311 fi[i*FI_STRIDE+XX] += fx;
312 fi[i*FI_STRIDE+YY] += fy;
313 fi[i*FI_STRIDE+ZZ] += fz;
314 /* Decrement j-atom force */
315 f[aj*F_STRIDE+XX] -= fx;
316 f[aj*F_STRIDE+YY] -= fy;
317 f[aj*F_STRIDE+ZZ] -= fz;
318 /* 9 flops for force addition */