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39 * \brief This file contains function definitions necessary for
40 * computing energies and forces for the plain-Ewald long-ranged part,
41 * and the correction for overall system charge for all Ewald-family
44 * \author David van der Spoel <david.vanderspoel@icm.uu.se>
45 * \author Mark Abraham <mark.j.abraham@gmail.com>
46 * \ingroup module_ewald
59 #include "gromacs/math/functions.h"
60 #include "gromacs/math/gmxcomplex.h"
61 #include "gromacs/math/units.h"
62 #include "gromacs/math/utilities.h"
63 #include "gromacs/math/vec.h"
64 #include "gromacs/math/vectypes.h"
65 #include "gromacs/mdtypes/commrec.h"
66 #include "gromacs/mdtypes/inputrec.h"
67 #include "gromacs/mdtypes/md_enums.h"
68 #include "gromacs/utility/fatalerror.h"
69 #include "gromacs/utility/smalloc.h"
71 struct gmx_ewald_tab_t
75 t_complex *tab_xy, *tab_qxyz;
78 void init_ewald_tab(struct gmx_ewald_tab_t **et, const t_inputrec *ir, FILE *fp)
83 fprintf(fp, "Will do ordinary reciprocal space Ewald sum.\n");
86 (*et)->nx = ir->nkx+1;
87 (*et)->ny = ir->nky+1;
88 (*et)->nz = ir->nkz+1;
89 (*et)->kmax = std::max((*et)->nx, std::max((*et)->ny, (*et)->nz));
92 (*et)->tab_qxyz = NULL;
95 //! Calculates wave vectors.
96 static void calc_lll(const rvec box, rvec lll)
98 lll[XX] = 2.0*M_PI/box[XX];
99 lll[YY] = 2.0*M_PI/box[YY];
100 lll[ZZ] = 2.0*M_PI/box[ZZ];
103 //! Make tables for the structure factor parts
104 static void tabulateStructureFactors(int natom, rvec x[], int kmax, cvec **eir, rvec lll)
110 printf("Go away! kmax = %d\n", kmax);
114 for (i = 0; (i < natom); i++)
116 for (m = 0; (m < 3); m++)
122 for (m = 0; (m < 3); m++)
124 eir[1][i][m].re = cos(x[i][m]*lll[m]);
125 eir[1][i][m].im = sin(x[i][m]*lll[m]);
127 for (j = 2; (j < kmax); j++)
129 for (m = 0; (m < 3); m++)
131 eir[j][i][m] = cmul(eir[j-1][i][m], eir[1][i][m]);
137 real do_ewald(t_inputrec *ir,
139 real chargeA[], real chargeB[],
141 t_commrec *cr, int natoms,
142 matrix lrvir, real ewaldcoeff,
143 real lambda, real *dvdlambda,
144 struct gmx_ewald_tab_t *et)
146 real factor = -1.0/(4*ewaldcoeff*ewaldcoeff);
147 real scaleRecip = 4.0*M_PI/(box[XX]*box[YY]*box[ZZ])*ONE_4PI_EPS0/ir->epsilon_r; /* 1/(Vol*e0) */
148 real *charge, energy_AB[2], energy;
150 int lowiy, lowiz, ix, iy, iz, n, q;
151 real tmp, cs, ss, ak, akv, mx, my, mz, m2, scale;
152 gmx_bool bFreeEnergy;
158 gmx_fatal(FARGS, "No parallel Ewald. Use PME instead.\n");
163 if (!et->eir) /* allocate if we need to */
165 snew(et->eir, et->kmax);
166 for (n = 0; n < et->kmax; n++)
168 snew(et->eir[n], natoms);
170 snew(et->tab_xy, natoms);
171 snew(et->tab_qxyz, natoms);
174 bFreeEnergy = (ir->efep != efepNO);
179 tabulateStructureFactors(natoms, x, et->kmax, et->eir, lll);
181 for (q = 0; q < (bFreeEnergy ? 2 : 1); q++)
191 scale = 1.0 - lambda;
201 for (ix = 0; ix < et->nx; ix++)
204 for (iy = lowiy; iy < et->ny; iy++)
209 for (n = 0; n < natoms; n++)
211 et->tab_xy[n] = cmul(et->eir[ix][n][XX], et->eir[iy][n][YY]);
216 for (n = 0; n < natoms; n++)
218 et->tab_xy[n] = cmul(et->eir[ix][n][XX], conjugate(et->eir[-iy][n][YY]));
221 for (iz = lowiz; iz < et->nz; iz++)
224 m2 = mx*mx+my*my+mz*mz;
225 ak = exp(m2*factor)/m2;
226 akv = 2.0*ak*(1.0/m2-factor);
229 for (n = 0; n < natoms; n++)
231 et->tab_qxyz[n] = rcmul(charge[n], cmul(et->tab_xy[n],
232 et->eir[iz][n][ZZ]));
237 for (n = 0; n < natoms; n++)
239 et->tab_qxyz[n] = rcmul(charge[n], cmul(et->tab_xy[n],
240 conjugate(et->eir[-iz][n][ZZ])));
245 for (n = 0; n < natoms; n++)
247 cs += et->tab_qxyz[n].re;
248 ss += et->tab_qxyz[n].im;
250 energy_AB[q] += ak*(cs*cs+ss*ss);
251 tmp = scale*akv*(cs*cs+ss*ss);
252 lrvir[XX][XX] -= tmp*mx*mx;
253 lrvir[XX][YY] -= tmp*mx*my;
254 lrvir[XX][ZZ] -= tmp*mx*mz;
255 lrvir[YY][YY] -= tmp*my*my;
256 lrvir[YY][ZZ] -= tmp*my*mz;
257 lrvir[ZZ][ZZ] -= tmp*mz*mz;
258 for (n = 0; n < natoms; n++)
260 /*tmp=scale*ak*(cs*tab_qxyz[n].im-ss*tab_qxyz[n].re);*/
261 tmp = scale*ak*(cs*et->tab_qxyz[n].im-ss*et->tab_qxyz[n].re);
262 f[n][XX] += tmp*mx*2*scaleRecip;
263 f[n][YY] += tmp*my*2*scaleRecip;
264 f[n][ZZ] += tmp*mz*2*scaleRecip;
280 energy = energy_AB[0];
284 energy = (1.0 - lambda)*energy_AB[0] + lambda*energy_AB[1];
285 *dvdlambda += scaleRecip*(energy_AB[1] - energy_AB[0]);
288 lrvir[XX][XX] = -0.5*scaleRecip*(lrvir[XX][XX]+energy);
289 lrvir[XX][YY] = -0.5*scaleRecip*(lrvir[XX][YY]);
290 lrvir[XX][ZZ] = -0.5*scaleRecip*(lrvir[XX][ZZ]);
291 lrvir[YY][YY] = -0.5*scaleRecip*(lrvir[YY][YY]+energy);
292 lrvir[YY][ZZ] = -0.5*scaleRecip*(lrvir[YY][ZZ]);
293 lrvir[ZZ][ZZ] = -0.5*scaleRecip*(lrvir[ZZ][ZZ]+energy);
295 lrvir[YY][XX] = lrvir[XX][YY];
296 lrvir[ZZ][XX] = lrvir[XX][ZZ];
297 lrvir[ZZ][YY] = lrvir[YY][ZZ];
299 energy *= scaleRecip;
304 real ewald_charge_correction(t_commrec *cr, t_forcerec *fr, real lambda,
306 real *dvdlambda, tensor vir)
309 real vol, fac, qs2A, qs2B, vc, enercorr;
314 /* Apply charge correction */
315 vol = box[XX][XX]*box[YY][YY]*box[ZZ][ZZ];
317 fac = M_PI*ONE_4PI_EPS0/(fr->epsilon_r*2.0*vol*vol*gmx::square(fr->ewaldcoeff_q));
319 qs2A = fr->qsum[0]*fr->qsum[0];
320 qs2B = fr->qsum[1]*fr->qsum[1];
322 vc = (qs2A*(1 - lambda) + qs2B*lambda)*fac;
326 *dvdlambda += -vol*(qs2B - qs2A)*fac;
328 for (d = 0; d < DIM; d++)
335 fprintf(debug, "Total charge correction: Vcharge=%g\n", enercorr);