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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
58 #include "gromacs/ewald/ewald_utils.h"
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/forcerec.h"
67 #include "gromacs/mdtypes/inputrec.h"
68 #include "gromacs/mdtypes/md_enums.h"
69 #include "gromacs/utility/fatalerror.h"
70 #include "gromacs/utility/smalloc.h"
72 struct gmx_ewald_tab_t
76 t_complex *tab_xy, *tab_qxyz;
79 void init_ewald_tab(struct gmx_ewald_tab_t** et, const t_inputrec* ir, FILE* fp)
84 fprintf(fp, "Will do ordinary reciprocal space Ewald sum.\n");
87 (*et)->nx = ir->nkx + 1;
88 (*et)->ny = ir->nky + 1;
89 (*et)->nz = ir->nkz + 1;
90 (*et)->kmax = std::max((*et)->nx, std::max((*et)->ny, (*et)->nz));
92 (*et)->tab_xy = nullptr;
93 (*et)->tab_qxyz = nullptr;
96 //! Calculates wave vectors.
97 static void calc_lll(const rvec box, rvec lll)
99 lll[XX] = 2.0 * M_PI / box[XX];
100 lll[YY] = 2.0 * M_PI / box[YY];
101 lll[ZZ] = 2.0 * M_PI / box[ZZ];
104 //! Make tables for the structure factor parts
105 static void tabulateStructureFactors(int natom, const rvec x[], int kmax, cvec** eir, const rvec lll)
111 printf("Go away! kmax = %d\n", kmax);
115 for (i = 0; (i < natom); i++)
117 for (m = 0; (m < 3); m++)
123 for (m = 0; (m < 3); m++)
125 eir[1][i][m].re = std::cos(x[i][m] * lll[m]);
126 eir[1][i][m].im = std::sin(x[i][m] * lll[m]);
128 for (j = 2; (j < kmax); j++)
130 for (m = 0; (m < 3); m++)
132 eir[j][i][m] = cmul(eir[j - 1][i][m], eir[1][i][m]);
138 real do_ewald(const t_inputrec* ir,
141 const real chargeA[],
142 const real chargeB[],
152 real factor = -1.0 / (4 * ewaldcoeff * ewaldcoeff);
154 real energy_AB[2], energy;
156 int lowiy, lowiz, ix, iy, iz, n, q;
157 real tmp, cs, ss, ak, akv, mx, my, mz, m2, scale;
158 gmx_bool bFreeEnergy;
164 gmx_fatal(FARGS, "No parallel Ewald. Use PME instead.\n");
168 /* Scale box with Ewald wall factor */
170 EwaldBoxZScaler boxScaler(*ir);
171 boxScaler.scaleBox(box, scaledBox);
174 for (int i = 0; (i < DIM); i++)
176 boxDiag[i] = scaledBox[i][i];
180 real scaleRecip = 4.0 * M_PI / (boxDiag[XX] * boxDiag[YY] * boxDiag[ZZ]) * ONE_4PI_EPS0 / ir->epsilon_r;
182 if (!et->eir) /* allocate if we need to */
184 snew(et->eir, et->kmax);
185 for (n = 0; n < et->kmax; n++)
187 snew(et->eir[n], natoms);
189 snew(et->tab_xy, natoms);
190 snew(et->tab_qxyz, natoms);
193 bFreeEnergy = (ir->efep != efepNO);
197 calc_lll(boxDiag, lll);
198 tabulateStructureFactors(natoms, x, et->kmax, et->eir, lll);
200 for (q = 0; q < (bFreeEnergy ? 2 : 1); q++)
210 scale = 1.0 - lambda;
220 for (ix = 0; ix < et->nx; ix++)
223 for (iy = lowiy; iy < et->ny; iy++)
228 for (n = 0; n < natoms; n++)
230 et->tab_xy[n] = cmul(et->eir[ix][n][XX], et->eir[iy][n][YY]);
235 for (n = 0; n < natoms; n++)
237 et->tab_xy[n] = cmul(et->eir[ix][n][XX], conjugate(et->eir[-iy][n][YY]));
240 for (iz = lowiz; iz < et->nz; iz++)
243 m2 = mx * mx + my * my + mz * mz;
244 ak = std::exp(m2 * factor) / m2;
245 akv = 2.0 * ak * (1.0 / m2 - factor);
248 for (n = 0; n < natoms; n++)
250 et->tab_qxyz[n] = rcmul(charge[n], cmul(et->tab_xy[n], et->eir[iz][n][ZZ]));
255 for (n = 0; n < natoms; n++)
257 et->tab_qxyz[n] = rcmul(
258 charge[n], cmul(et->tab_xy[n], conjugate(et->eir[-iz][n][ZZ])));
263 for (n = 0; n < natoms; n++)
265 cs += et->tab_qxyz[n].re;
266 ss += et->tab_qxyz[n].im;
268 energy_AB[q] += ak * (cs * cs + ss * ss);
269 tmp = scale * akv * (cs * cs + ss * ss);
270 lrvir[XX][XX] -= tmp * mx * mx;
271 lrvir[XX][YY] -= tmp * mx * my;
272 lrvir[XX][ZZ] -= tmp * mx * mz;
273 lrvir[YY][YY] -= tmp * my * my;
274 lrvir[YY][ZZ] -= tmp * my * mz;
275 lrvir[ZZ][ZZ] -= tmp * mz * mz;
276 for (n = 0; n < natoms; n++)
278 /*tmp=scale*ak*(cs*tab_qxyz[n].im-ss*tab_qxyz[n].re);*/
279 tmp = scale * ak * (cs * et->tab_qxyz[n].im - ss * et->tab_qxyz[n].re);
280 f[n][XX] += tmp * mx * 2 * scaleRecip;
281 f[n][YY] += tmp * my * 2 * scaleRecip;
282 f[n][ZZ] += tmp * mz * 2 * scaleRecip;
298 energy = energy_AB[0];
302 energy = (1.0 - lambda) * energy_AB[0] + lambda * energy_AB[1];
303 *dvdlambda += scaleRecip * (energy_AB[1] - energy_AB[0]);
306 lrvir[XX][XX] = -0.5 * scaleRecip * (lrvir[XX][XX] + energy);
307 lrvir[XX][YY] = -0.5 * scaleRecip * (lrvir[XX][YY]);
308 lrvir[XX][ZZ] = -0.5 * scaleRecip * (lrvir[XX][ZZ]);
309 lrvir[YY][YY] = -0.5 * scaleRecip * (lrvir[YY][YY] + energy);
310 lrvir[YY][ZZ] = -0.5 * scaleRecip * (lrvir[YY][ZZ]);
311 lrvir[ZZ][ZZ] = -0.5 * scaleRecip * (lrvir[ZZ][ZZ] + energy);
313 lrvir[YY][XX] = lrvir[XX][YY];
314 lrvir[ZZ][XX] = lrvir[XX][ZZ];
315 lrvir[ZZ][YY] = lrvir[YY][ZZ];
317 energy *= scaleRecip;
322 real ewald_charge_correction(const t_commrec* cr,
323 const t_forcerec* fr,
330 real vol, fac, qs2A, qs2B, vc, enercorr;
335 /* Apply charge correction */
336 vol = box[XX][XX] * box[YY][YY] * box[ZZ][ZZ];
338 fac = M_PI * ONE_4PI_EPS0
339 / (fr->ic->epsilon_r * 2.0 * vol * vol * gmx::square(fr->ic->ewaldcoeff_q));
341 qs2A = fr->qsum[0] * fr->qsum[0];
342 qs2B = fr->qsum[1] * fr->qsum[1];
344 vc = (qs2A * (1 - lambda) + qs2B * lambda) * fac;
346 enercorr = -vol * vc;
348 *dvdlambda += -vol * (qs2B - qs2A) * fac;
350 for (d = 0; d < DIM; d++)
357 fprintf(debug, "Total charge correction: Vcharge=%g\n", enercorr);