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40 * \brief This file contains function definitions necessary for
41 * computing energies and forces for the plain-Ewald long-ranged part,
42 * and the correction for overall system charge for all Ewald-family
45 * \author David van der Spoel <david.vanderspoel@icm.uu.se>
46 * \author Mark Abraham <mark.j.abraham@gmail.com>
47 * \ingroup module_ewald
59 #include "gromacs/ewald/ewald_utils.h"
60 #include "gromacs/math/functions.h"
61 #include "gromacs/math/gmxcomplex.h"
62 #include "gromacs/math/units.h"
63 #include "gromacs/math/utilities.h"
64 #include "gromacs/math/vec.h"
65 #include "gromacs/math/vectypes.h"
66 #include "gromacs/mdtypes/commrec.h"
67 #include "gromacs/mdtypes/forcerec.h"
68 #include "gromacs/mdtypes/inputrec.h"
69 #include "gromacs/mdtypes/interaction_const.h"
70 #include "gromacs/mdtypes/md_enums.h"
71 #include "gromacs/utility/arrayref.h"
72 #include "gromacs/utility/fatalerror.h"
73 #include "gromacs/utility/smalloc.h"
75 using cvec = std::array<t_complex, DIM>;
77 gmx_ewald_tab_t::gmx_ewald_tab_t(const t_inputrec& ir, FILE* fp)
81 fprintf(fp, "Will do ordinary reciprocal space Ewald sum.\n");
87 kmax = std::max(nx, std::max(ny, nz));
90 gmx_ewald_tab_t::~gmx_ewald_tab_t() = default;
92 //! Calculates wave vectors.
93 static void calc_lll(const rvec box, rvec lll)
95 lll[XX] = 2.0 * M_PI / box[XX];
96 lll[YY] = 2.0 * M_PI / box[YY];
97 lll[ZZ] = 2.0 * M_PI / box[ZZ];
100 //! Make tables for the structure factor parts
101 static void tabulateStructureFactors(int natom, gmx::ArrayRef<const gmx::RVec> x, int kmax, cvec** eir, const rvec lll)
107 printf("Go away! kmax = %d\n", kmax);
111 for (i = 0; (i < natom); i++)
113 for (m = 0; (m < 3); m++)
119 for (m = 0; (m < 3); m++)
121 eir[1][i][m].re = std::cos(x[i][m] * lll[m]);
122 eir[1][i][m].im = std::sin(x[i][m] * lll[m]);
124 for (j = 2; (j < kmax); j++)
126 for (m = 0; (m < 3); m++)
128 eir[j][i][m] = cmul(eir[j - 1][i][m], eir[1][i][m]);
134 real do_ewald(bool havePbcXY2Walls,
137 FreeEnergyPerturbationType freeEnergyPerturbationType,
138 gmx::ArrayRef<const gmx::RVec> coords,
139 gmx::ArrayRef<gmx::RVec> forces,
140 gmx::ArrayRef<const real> chargeA,
141 gmx::ArrayRef<const real> chargeB,
143 const t_commrec* commrec,
151 real factor = -1.0 / (4 * ewaldcoeff * ewaldcoeff);
152 real energy_AB[2], energy;
154 int lowiy, lowiz, ix, iy, iz, n, q;
155 real tmp, cs, ss, ak, akv, mx, my, mz, m2, scale;
159 if (commrec != nullptr)
163 gmx_fatal(FARGS, "No parallel Ewald. Use PME instead.\n");
167 /* Scale box with Ewald wall factor */
169 EwaldBoxZScaler boxScaler(havePbcXY2Walls, wallEwaldZfac);
170 boxScaler.scaleBox(box, scaledBox);
173 for (int i = 0; (i < DIM); i++)
175 boxDiag[i] = scaledBox[i][i];
179 real scaleRecip = 4.0 * M_PI / (boxDiag[XX] * boxDiag[YY] * boxDiag[ZZ]) * gmx::c_one4PiEps0 / epsilonR;
182 for (n = 0; n < et->kmax; n++)
184 snew(eir[n], natoms);
186 et->tab_xy.resize(natoms);
187 et->tab_qxyz.resize(natoms);
189 bFreeEnergy = (freeEnergyPerturbationType != FreeEnergyPerturbationType::No);
193 calc_lll(boxDiag, lll);
194 tabulateStructureFactors(natoms, coords, et->kmax, eir, lll);
196 gmx::ArrayRef<const real> charge;
197 for (q = 0; q < (bFreeEnergy ? 2 : 1); q++)
207 scale = 1.0 - lambda;
217 for (ix = 0; ix < et->nx; ix++)
220 for (iy = lowiy; iy < et->ny; iy++)
225 for (n = 0; n < natoms; n++)
227 et->tab_xy[n] = cmul(eir[ix][n][XX], eir[iy][n][YY]);
232 for (n = 0; n < natoms; n++)
234 et->tab_xy[n] = cmul(eir[ix][n][XX], conjugate(eir[-iy][n][YY]));
237 for (iz = lowiz; iz < et->nz; iz++)
240 m2 = mx * mx + my * my + mz * mz;
241 ak = std::exp(m2 * factor) / m2;
242 akv = 2.0 * ak * (1.0 / m2 - factor);
245 for (n = 0; n < natoms; n++)
247 et->tab_qxyz[n] = rcmul(charge[n], cmul(et->tab_xy[n], eir[iz][n][ZZ]));
252 for (n = 0; n < natoms; n++)
255 rcmul(charge[n], cmul(et->tab_xy[n], conjugate(eir[-iz][n][ZZ])));
260 for (n = 0; n < natoms; n++)
262 cs += et->tab_qxyz[n].re;
263 ss += et->tab_qxyz[n].im;
265 energy_AB[q] += ak * (cs * cs + ss * ss);
266 tmp = scale * akv * (cs * cs + ss * ss);
267 lrvir[XX][XX] -= tmp * mx * mx;
268 lrvir[XX][YY] -= tmp * mx * my;
269 lrvir[XX][ZZ] -= tmp * mx * mz;
270 lrvir[YY][YY] -= tmp * my * my;
271 lrvir[YY][ZZ] -= tmp * my * mz;
272 lrvir[ZZ][ZZ] -= tmp * mz * mz;
273 for (n = 0; n < natoms; n++)
275 /*tmp=scale*ak*(cs*tab_qxyz[n].im-ss*tab_qxyz[n].re);*/
276 tmp = scale * ak * (cs * et->tab_qxyz[n].im - ss * et->tab_qxyz[n].re);
277 forces[n][XX] += tmp * mx * 2 * scaleRecip;
278 forces[n][YY] += tmp * my * 2 * scaleRecip;
279 forces[n][ZZ] += tmp * mz * 2 * scaleRecip;
290 energy = energy_AB[0];
294 energy = (1.0 - lambda) * energy_AB[0] + lambda * energy_AB[1];
295 *dvdlambda += scaleRecip * (energy_AB[1] - energy_AB[0]);
298 lrvir[XX][XX] = -0.5 * scaleRecip * (lrvir[XX][XX] + energy);
299 lrvir[XX][YY] = -0.5 * scaleRecip * (lrvir[XX][YY]);
300 lrvir[XX][ZZ] = -0.5 * scaleRecip * (lrvir[XX][ZZ]);
301 lrvir[YY][YY] = -0.5 * scaleRecip * (lrvir[YY][YY] + energy);
302 lrvir[YY][ZZ] = -0.5 * scaleRecip * (lrvir[YY][ZZ]);
303 lrvir[ZZ][ZZ] = -0.5 * scaleRecip * (lrvir[ZZ][ZZ] + energy);
305 lrvir[YY][XX] = lrvir[XX][YY];
306 lrvir[ZZ][XX] = lrvir[XX][ZZ];
307 lrvir[ZZ][YY] = lrvir[YY][ZZ];
309 energy *= scaleRecip;
314 real ewald_charge_correction(const t_commrec* commrec,
316 const real ewaldcoeffQ,
317 gmx::ArrayRef<const double> qsum,
328 /* Apply charge correction */
329 real vol = box[XX][XX] * box[YY][YY] * box[ZZ][ZZ];
331 real fac = M_PI * gmx::c_one4PiEps0 / (epsilonR * 2.0 * vol * vol * gmx::square(ewaldcoeffQ));
333 real qs2A = qsum[0] * qsum[0];
334 real qs2B = qsum[1] * qsum[1];
336 real vc = (qs2A * (1 - lambda) + qs2B * lambda) * fac;
338 enercorr = -vol * vc;
340 *dvdlambda += -vol * (qs2B - qs2A) * fac;
342 for (int d = 0; d < DIM; d++)