src/gromacs/gmxlib/ewald_util.c

   1 /*
   2  * This file is part of the GROMACS molecular simulation package.
   3  *
   4  * Copyright (c) 1991-2000, University of Groningen, The Netherlands.
   5  * Copyright (c) 2001-2004, The GROMACS development team.
   6  * Copyright (c) 2013,2014, by the GROMACS development team, led by
   7  * Mark Abraham, David van der Spoel, Berk Hess, and Erik Lindahl,
   8  * and including many others, as listed in the AUTHORS file in the
   9  * top-level source directory and at http://www.gromacs.org.
  10  *
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  12  * modify it under the terms of the GNU Lesser General Public License
  13  * as published by the Free Software Foundation; either version 2.1
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  37 #include "gmxpre.h"
  38
  39 #include "config.h"
  40
  41 #include <stdio.h>
  42 #include <math.h>
  43 #include "gromacs/math/utilities.h"
  44 #include "gromacs/legacyheaders/typedefs.h"
  45 #include "gromacs/legacyheaders/types/commrec.h"
  46 #include "gromacs/math/vec.h"
  47 #include "gromacs/legacyheaders/coulomb.h"
  48 #include "gromacs/utility/smalloc.h"
  49 #include "gromacs/math/units.h"
  50 #include "gromacs/legacyheaders/txtdump.h"
  51 #include "gromacs/utility/futil.h"
  52 #include "gromacs/legacyheaders/names.h"
  53 #include "gromacs/legacyheaders/macros.h"
  54
  55 real calc_ewaldcoeff_q(real rc, real dtol)
  56 {
  57     real x = 5, low, high;
  58     int  n, i = 0;
  59
  60
  61     do
  62     {
  63         i++;
  64         x *= 2;
  65     }
  66     while (gmx_erfc(x*rc) > dtol);
  67
  68     n    = i+60; /* search tolerance is 2^-60 */
  69     low  = 0;
  70     high = x;
  71     for (i = 0; i < n; i++)
  72     {
  73         x = (low+high)/2;
  74         if (gmx_erfc(x*rc) > dtol)
  75         {
  76             low = x;
  77         }
  78         else
  79         {
  80             high = x;
  81         }
  82     }
  83     return x;
  84 }
  85
  86 static real ewald_function_lj(real x, real rc)
  87 {
  88     real xrc, xrc2, xrc4, factor;
  89     xrc  = x*rc;
  90     xrc2 = xrc*xrc;
  91     xrc4 = xrc2*xrc2;
  92 #ifdef GMX_DOUBLE
  93     factor = exp(-xrc2)*(1 + xrc2 + xrc4/2.0);
  94 #else
  95     factor = expf(-xrc2)*(1 + xrc2 + xrc4/2.0);
  96 #endif
  97
  98     return factor;
  99 }
 100
 101 real calc_ewaldcoeff_lj(real rc, real dtol)
 102 {
 103     real x = 5, low, high;
 104     int  n, i = 0;
 105
 106     do
 107     {
 108         i++;
 109         x *= 2.0;
 110     }
 111     while (ewald_function_lj(x, rc) > dtol);
 112
 113     n    = i + 60; /* search tolerance is 2^-60 */
 114     low  = 0;
 115     high = x;
 116     for (i = 0; i < n; ++i)
 117     {
 118         x = (low + high) / 2.0;
 119         if (ewald_function_lj(x, rc) > dtol)
 120         {
 121             low = x;
 122         }
 123         else
 124         {
 125             high = x;
 126         }
 127     }
 128     return x;
 129 }
 130
 131 void ewald_LRcorrection(int start, int end,
 132                         t_commrec *cr, int thread, t_forcerec *fr,
 133                         real *chargeA, real *chargeB,
 134                         real *C6A, real *C6B,
 135                         real *sigmaA, real *sigmaB,
 136                         real *sigma3A, real *sigma3B,
 137                         gmx_bool calc_excl_corr,
 138                         t_blocka *excl, rvec x[],
 139                         matrix box, rvec mu_tot[],
 140                         int ewald_geometry, real epsilon_surface,
 141                         rvec *f, tensor vir_q, tensor vir_lj,
 142                         real *Vcorr_q, real *Vcorr_lj,
 143                         real lambda_q, real lambda_lj,
 144                         real *dvdlambda_q, real *dvdlambda_lj)
 145 {
 146     int         i, i1, i2, j, k, m, iv, jv, q;
 147     atom_id    *AA;
 148     double      Vexcl_q, dvdl_excl_q, dvdl_excl_lj; /* Necessary for precision */
 149     double      Vexcl_lj;
 150     real        one_4pi_eps;
 151     real        v, vc, qiA, qiB, dr2, rinv, enercorr;
 152     real        Vself_q[2], Vself_lj[2], Vdipole[2], rinv2, ewc_q = fr->ewaldcoeff_q, ewcdr;
 153     real        ewc_lj = fr->ewaldcoeff_lj, ewc_lj2 = ewc_lj * ewc_lj;
 154     real        c6Ai   = 0, c6Bi = 0, c6A = 0, c6B = 0, ewcdr2, ewcdr4, c6L = 0, rinv6;
 155     rvec        df, dx, mutot[2], dipcorrA, dipcorrB;
 156     tensor      dxdf_q, dxdf_lj;
 157     real        vol = box[XX][XX]*box[YY][YY]*box[ZZ][ZZ];
 158     real        L1_q, L1_lj, dipole_coeff, qqA, qqB, qqL, vr0_q, vr0_lj = 0;
 159     gmx_bool    bFreeEnergy  = (chargeB != NULL);
 160     gmx_bool    bMolPBC      = fr->bMolPBC;
 161     gmx_bool    bDoingLBRule = (fr->ljpme_combination_rule == eljpmeLB);
 162
 163     /* This routine can be made faster by using tables instead of analytical interactions
 164      * However, that requires a thorough verification that they are correct in all cases.
 165      */
 166
 167     one_4pi_eps   = ONE_4PI_EPS0/fr->epsilon_r;
 168     vr0_q         = ewc_q*M_2_SQRTPI;
 169     if (EVDW_PME(fr->vdwtype))
 170     {
 171         vr0_lj    = -pow(ewc_lj, 6)/6.0;
 172     }
 173
 174     AA           = excl->a;
 175     Vexcl_q      = 0;
 176     Vexcl_lj     = 0;
 177     dvdl_excl_q  = 0;
 178     dvdl_excl_lj = 0;
 179     Vdipole[0]   = 0;
 180     Vdipole[1]   = 0;
 181     L1_q         = 1.0-lambda_q;
 182     L1_lj        = 1.0-lambda_lj;
 183     /* Note that we have to transform back to gromacs units, since
 184      * mu_tot contains the dipole in debye units (for output).
 185      */
 186     for (i = 0; (i < DIM); i++)
 187     {
 188         mutot[0][i] = mu_tot[0][i]*DEBYE2ENM;
 189         mutot[1][i] = mu_tot[1][i]*DEBYE2ENM;
 190         dipcorrA[i] = 0;
 191         dipcorrB[i] = 0;
 192     }
 193     dipole_coeff = 0;
 194     switch (ewald_geometry)
 195     {
 196         case eewg3D:
 197             if (epsilon_surface != 0)
 198             {
 199                 dipole_coeff =
 200                     2*M_PI*ONE_4PI_EPS0/((2*epsilon_surface + fr->epsilon_r)*vol);
 201                 for (i = 0; (i < DIM); i++)
 202                 {
 203                     dipcorrA[i] = 2*dipole_coeff*mutot[0][i];
 204                     dipcorrB[i] = 2*dipole_coeff*mutot[1][i];
 205                 }
 206             }
 207             break;
 208         case eewg3DC:
 209             dipole_coeff = 2*M_PI*one_4pi_eps/vol;
 210             dipcorrA[ZZ] = 2*dipole_coeff*mutot[0][ZZ];
 211             dipcorrB[ZZ] = 2*dipole_coeff*mutot[1][ZZ];
 212             break;
 213         default:
 214             gmx_incons("Unsupported Ewald geometry");
 215             break;
 216     }
 217     if (debug)
 218     {
 219         fprintf(debug, "dipcorr = %8.3f  %8.3f  %8.3f\n",
 220                 dipcorrA[XX], dipcorrA[YY], dipcorrA[ZZ]);
 221         fprintf(debug, "mutot   = %8.3f  %8.3f  %8.3f\n",
 222                 mutot[0][XX], mutot[0][YY], mutot[0][ZZ]);
 223     }
 224     clear_mat(dxdf_q);
 225     if (EVDW_PME(fr->vdwtype))
 226     {
 227         clear_mat(dxdf_lj);
 228     }
 229     if ((calc_excl_corr || dipole_coeff != 0) && !bFreeEnergy)
 230     {
 231         for (i = start; (i < end); i++)
 232         {
 233             /* Initiate local variables (for this i-particle) to 0 */
 234             qiA = chargeA[i]*one_4pi_eps;
 235             if (EVDW_PME(fr->vdwtype))
 236             {
 237                 c6Ai = C6A[i];
 238                 if (bDoingLBRule)
 239                 {
 240                     c6Ai *= sigma3A[i];
 241                 }
 242             }
 243             if (calc_excl_corr)
 244             {
 245                 i1  = excl->index[i];
 246                 i2  = excl->index[i+1];
 247
 248                 /* Loop over excluded neighbours */
 249                 for (j = i1; (j < i2); j++)
 250                 {
 251                     k = AA[j];
 252                     /*
 253                      * First we must test whether k <> i, and then,
 254                      * because the exclusions are all listed twice i->k
 255                      * and k->i we must select just one of the two.  As
 256                      * a minor optimization we only compute forces when
 257                      * the charges are non-zero.
 258                      */
 259                     if (k > i)
 260                     {
 261                         qqA = qiA*chargeA[k];
 262                         if (EVDW_PME(fr->vdwtype))
 263                         {
 264                             c6A  = c6Ai * C6A[k];
 265                             if (bDoingLBRule)
 266                             {
 267                                 c6A *= pow(0.5*(sigmaA[i]+sigmaA[k]), 6)*sigma3A[k];
 268                             }
 269                         }
 270                         if (qqA != 0.0 || c6A != 0.0)
 271                         {
 272                             real fscal;
 273
 274                             fscal = 0;
 275                             rvec_sub(x[i], x[k], dx);
 276                             if (bMolPBC)
 277                             {
 278                                 /* Cheap pbc_dx, assume excluded pairs are at short distance. */
 279                                 for (m = DIM-1; (m >= 0); m--)
 280                                 {
 281                                     if (dx[m] > 0.5*box[m][m])
 282                                     {
 283                                         rvec_dec(dx, box[m]);
 284                                     }
 285                                     else if (dx[m] < -0.5*box[m][m])
 286                                     {
 287                                         rvec_inc(dx, box[m]);
 288                                     }
 289                                 }
 290                             }
 291                             dr2 = norm2(dx);
 292                             /* Distance between two excluded particles
 293                              * may be zero in the case of shells
 294                              */
 295                             if (dr2 != 0)
 296                             {
 297                                 rinv              = gmx_invsqrt(dr2);
 298                                 rinv2             = rinv*rinv;
 299                                 if (qqA != 0.0)
 300                                 {
 301                                     real dr;
 302
 303                                     dr       = 1.0/rinv;
 304                                     ewcdr    = ewc_q*dr;
 305                                     vc       = qqA*gmx_erf(ewcdr)*rinv;
 306                                     Vexcl_q += vc;
 307 #ifdef GMX_DOUBLE
 308                                     /* Relative accuracy at R_ERF_R_INACC of 3e-10 */
 309 #define       R_ERF_R_INACC 0.006
 310 #else
 311                                     /* Relative accuracy at R_ERF_R_INACC of 2e-5 */
 312 #define       R_ERF_R_INACC 0.1
 313 #endif
 314                                     /* fscal is the scalar force pre-multiplied by rinv,
 315                                      * to normalise the relative position vector dx */
 316                                     if (ewcdr > R_ERF_R_INACC)
 317                                     {
 318                                         fscal = rinv2*(vc - qqA*ewc_q*M_2_SQRTPI*exp(-ewcdr*ewcdr));
 319                                     }
 320                                     else
 321                                     {
 322                                         /* Use a fourth order series expansion for small ewcdr */
 323                                         fscal = ewc_q*ewc_q*qqA*vr0_q*(2.0/3.0 - 0.4*ewcdr*ewcdr);
 324                                     }
 325
 326                                     /* The force vector is obtained by multiplication with
 327                                      * the relative position vector
 328                                      */
 329                                     svmul(fscal, dx, df);
 330                                     rvec_inc(f[k], df);
 331                                     rvec_dec(f[i], df);
 332                                     for (iv = 0; (iv < DIM); iv++)
 333                                     {
 334                                         for (jv = 0; (jv < DIM); jv++)
 335                                         {
 336                                             dxdf_q[iv][jv] += dx[iv]*df[jv];
 337                                         }
 338                                     }
 339                                 }
 340
 341                                 if (c6A != 0.0)
 342                                 {
 343                                     rinv6     = rinv2*rinv2*rinv2;
 344                                     ewcdr2    = ewc_lj2*dr2;
 345                                     ewcdr4    = ewcdr2*ewcdr2;
 346                                     /* We get the excluded long-range contribution from -C6*(1-g(r))
 347                                      * g(r) is also defined in the manual under LJ-PME
 348                                      */
 349                                     vc        = -c6A*rinv6*(1.0 - exp(-ewcdr2)*(1 + ewcdr2 + 0.5*ewcdr4));
 350                                     Vexcl_lj += vc;
 351                                     /* The force is the derivative of the potential vc.
 352                                      * fscal is the scalar force pre-multiplied by rinv,
 353                                      * to normalise the relative position vector dx */
 354                                     fscal     = 6.0*vc*rinv2 + c6A*rinv6*exp(-ewcdr2)*ewc_lj2*ewcdr4;
 355
 356                                     /* The force vector is obtained by multiplication with
 357                                      * the relative position vector
 358                                      */
 359                                     svmul(fscal, dx, df);
 360                                     rvec_inc(f[k], df);
 361                                     rvec_dec(f[i], df);
 362                                     for (iv = 0; (iv < DIM); iv++)
 363                                     {
 364                                         for (jv = 0; (jv < DIM); jv++)
 365                                         {
 366                                             dxdf_lj[iv][jv] += dx[iv]*df[jv];
 367                                         }
 368                                     }
 369                                 }
 370                             }
 371                             else
 372                             {
 373                                 Vexcl_q  += qqA*vr0_q;
 374                                 Vexcl_lj += c6A*vr0_lj;
 375                             }
 376                         }
 377                     }
 378                 }
 379             }
 380             /* Dipole correction on force */
 381             if (dipole_coeff != 0)
 382             {
 383                 for (j = 0; (j < DIM); j++)
 384                 {
 385                     f[i][j] -= dipcorrA[j]*chargeA[i];
 386                 }
 387             }
 388         }
 389     }
 390     else if (calc_excl_corr || dipole_coeff != 0)
 391     {
 392         for (i = start; (i < end); i++)
 393         {
 394             /* Initiate local variables (for this i-particle) to 0 */
 395             qiA = chargeA[i]*one_4pi_eps;
 396             qiB = chargeB[i]*one_4pi_eps;
 397             if (EVDW_PME(fr->vdwtype))
 398             {
 399                 c6Ai = C6A[i];
 400                 c6Bi = C6B[i];
 401                 if (bDoingLBRule)
 402                 {
 403                     c6Ai *= sigma3A[i];
 404                     c6Bi *= sigma3B[i];
 405                 }
 406             }
 407             if (calc_excl_corr)
 408             {
 409                 i1  = excl->index[i];
 410                 i2  = excl->index[i+1];
 411
 412                 /* Loop over excluded neighbours */
 413                 for (j = i1; (j < i2); j++)
 414                 {
 415                     k = AA[j];
 416                     if (k > i)
 417                     {
 418                         qqA = qiA*chargeA[k];
 419                         qqB = qiB*chargeB[k];
 420                         if (EVDW_PME(fr->vdwtype))
 421                         {
 422                             c6A = c6Ai*C6A[k];
 423                             c6B = c6Bi*C6B[k];
 424                             if (bDoingLBRule)
 425                             {
 426                                 c6A *= pow(0.5*(sigmaA[i]+sigmaA[k]), 6)*sigma3A[k];
 427                                 c6B *= pow(0.5*(sigmaB[i]+sigmaB[k]), 6)*sigma3B[k];
 428                             }
 429                         }
 430                         if (qqA != 0.0 || qqB != 0.0 || c6A != 0.0 || c6B != 0.0)
 431                         {
 432                             real fscal;
 433
 434                             fscal = 0;
 435                             qqL   = L1_q*qqA + lambda_q*qqB;
 436                             if (EVDW_PME(fr->vdwtype))
 437                             {
 438                                 c6L = L1_lj*c6A + lambda_lj*c6B;
 439                             }
 440                             rvec_sub(x[i], x[k], dx);
 441                             if (bMolPBC)
 442                             {
 443                                 /* Cheap pbc_dx, assume excluded pairs are at short distance. */
 444                                 for (m = DIM-1; (m >= 0); m--)
 445                                 {
 446                                     if (dx[m] > 0.5*box[m][m])
 447                                     {
 448                                         rvec_dec(dx, box[m]);
 449                                     }
 450                                     else if (dx[m] < -0.5*box[m][m])
 451                                     {
 452                                         rvec_inc(dx, box[m]);
 453                                     }
 454                                 }
 455                             }
 456                             dr2 = norm2(dx);
 457                             if (dr2 != 0)
 458                             {
 459                                 rinv    = gmx_invsqrt(dr2);
 460                                 rinv2   = rinv*rinv;
 461                                 if (qqA != 0.0 || qqB != 0.0)
 462                                 {
 463                                     real dr;
 464
 465                                     dr           = 1.0/rinv;
 466                                     v            = gmx_erf(ewc_q*dr)*rinv;
 467                                     vc           = qqL*v;
 468                                     Vexcl_q     += vc;
 469                                     /* fscal is the scalar force pre-multiplied by rinv,
 470                                      * to normalise the relative position vector dx */
 471                                     fscal        = rinv2*(vc-qqL*ewc_q*M_2_SQRTPI*exp(-ewc_q*ewc_q*dr2));
 472                                     dvdl_excl_q += (qqB - qqA)*v;
 473
 474                                     /* The force vector is obtained by multiplication with
 475                                      * the relative position vector
 476                                      */
 477                                     svmul(fscal, dx, df);
 478                                     rvec_inc(f[k], df);
 479                                     rvec_dec(f[i], df);
 480                                     for (iv = 0; (iv < DIM); iv++)
 481                                     {
 482                                         for (jv = 0; (jv < DIM); jv++)
 483                                         {
 484                                             dxdf_q[iv][jv] += dx[iv]*df[jv];
 485                                         }
 486                                     }
 487                                 }
 488
 489                                 if ((c6A != 0.0 || c6B != 0.0) && EVDW_PME(fr->vdwtype))
 490                                 {
 491                                     rinv6         = rinv2*rinv2*rinv2;
 492                                     ewcdr2        = ewc_lj2*dr2;
 493                                     ewcdr4        = ewcdr2*ewcdr2;
 494                                     v             = -rinv6*(1.0 - exp(-ewcdr2)*(1 + ewcdr2 + 0.5*ewcdr4));
 495                                     vc            = c6L*v;
 496                                     Vexcl_lj     += vc;
 497                                     /* fscal is the scalar force pre-multiplied by rinv,
 498                                      * to normalise the relative position vector dx */
 499                                     fscal         = 6.0*vc*rinv2 + c6L*rinv6*exp(-ewcdr2)*ewc_lj2*ewcdr4;
 500                                     dvdl_excl_lj += (c6B - c6A)*v;
 501
 502                                     /* The force vector is obtained by multiplication with
 503                                      * the relative position vector
 504                                      */
 505                                     svmul(fscal, dx, df);
 506                                     rvec_inc(f[k], df);
 507                                     rvec_dec(f[i], df);
 508                                     for (iv = 0; (iv < DIM); iv++)
 509                                     {
 510                                         for (jv = 0; (jv < DIM); jv++)
 511                                         {
 512                                             dxdf_lj[iv][jv] += dx[iv]*df[jv];
 513                                         }
 514                                     }
 515                                 }
 516                             }
 517                             else
 518                             {
 519                                 Vexcl_q      += qqL*vr0_q;
 520                                 dvdl_excl_q  += (qqB - qqA)*vr0_q;
 521                                 Vexcl_lj     += c6L*vr0_lj;
 522                                 dvdl_excl_lj += (c6B - c6A)*vr0_lj;
 523                             }
 524                         }
 525                     }
 526                 }
 527             }
 528             /* Dipole correction on force */
 529             if (dipole_coeff != 0)
 530             {
 531                 for (j = 0; (j < DIM); j++)
 532                 {
 533                     f[i][j] -= L1_q*dipcorrA[j]*chargeA[i]
 534                         + lambda_q*dipcorrB[j]*chargeB[i];
 535                 }
 536             }
 537         }
 538     }
 539     for (iv = 0; (iv < DIM); iv++)
 540     {
 541         for (jv = 0; (jv < DIM); jv++)
 542         {
 543             vir_q[iv][jv]  += 0.5*dxdf_q[iv][jv];
 544             vir_lj[iv][jv] += 0.5*dxdf_lj[iv][jv];
 545         }
 546     }
 547
 548     Vself_q[0]  = 0;
 549     Vself_q[1]  = 0;
 550     Vself_lj[0] = 0;
 551     Vself_lj[1] = 0;
 552
 553     /* Global corrections only on master process */
 554     if (MASTER(cr) && thread == 0)
 555     {
 556         for (q = 0; q < (bFreeEnergy ? 2 : 1); q++)
 557         {
 558             if (calc_excl_corr)
 559             {
 560                 /* Self-energy correction */
 561                 Vself_q[q] = ewc_q*one_4pi_eps*fr->q2sum[q]*M_1_SQRTPI;
 562                 if (EVDW_PME(fr->vdwtype))
 563                 {
 564                     Vself_lj[q] =  fr->c6sum[q]*0.5*vr0_lj;
 565                 }
 566             }
 567
 568             /* Apply surface dipole correction:
 569              * correction = dipole_coeff * (dipole)^2
 570              */
 571             if (dipole_coeff != 0)
 572             {
 573                 if (ewald_geometry == eewg3D)
 574                 {
 575                     Vdipole[q] = dipole_coeff*iprod(mutot[q], mutot[q]);
 576                 }
 577                 else if (ewald_geometry == eewg3DC)
 578                 {
 579                     Vdipole[q] = dipole_coeff*mutot[q][ZZ]*mutot[q][ZZ];
 580                 }
 581             }
 582         }
 583     }
 584     if (!bFreeEnergy)
 585     {
 586         *Vcorr_q = Vdipole[0] - Vself_q[0] - Vexcl_q;
 587         if (EVDW_PME(fr->vdwtype))
 588         {
 589             *Vcorr_lj = -Vself_lj[0] - Vexcl_lj;
 590         }
 591     }
 592     else
 593     {
 594         *Vcorr_q = L1_q*(Vdipole[0] - Vself_q[0])
 595             + lambda_q*(Vdipole[1] - Vself_q[1])
 596             - Vexcl_q;
 597         *dvdlambda_q += Vdipole[1] - Vself_q[1]
 598             - (Vdipole[0] - Vself_q[0]) - dvdl_excl_q;
 599         if (EVDW_PME(fr->vdwtype))
 600         {
 601             *Vcorr_lj      = -(L1_lj*Vself_lj[0] + lambda_lj*Vself_lj[1]) - Vexcl_lj;
 602             *dvdlambda_lj += -Vself_lj[1] + Vself_lj[0] - dvdl_excl_lj;
 603         }
 604     }
 605
 606     if (debug)
 607     {
 608         fprintf(debug, "Long Range corrections for Ewald interactions:\n");
 609         fprintf(debug, "start=%d,natoms=%d\n", start, end-start);
 610         fprintf(debug, "q2sum = %g, Vself_q=%g c6sum = %g, Vself_lj=%g\n",
 611                 L1_q*fr->q2sum[0]+lambda_q*fr->q2sum[1], L1_q*Vself_q[0]+lambda_q*Vself_q[1], L1_lj*fr->c6sum[0]+lambda_lj*fr->c6sum[1], L1_lj*Vself_lj[0]+lambda_lj*Vself_lj[1]);
 612         fprintf(debug, "Electrostatic Long Range correction: Vexcl=%g\n", Vexcl_q);
 613         fprintf(debug, "Lennard-Jones Long Range correction: Vexcl=%g\n", Vexcl_lj);
 614         if (MASTER(cr) && thread == 0)
 615         {
 616             if (epsilon_surface > 0 || ewald_geometry == eewg3DC)
 617             {
 618                 fprintf(debug, "Total dipole correction: Vdipole=%g\n",
 619                         L1_q*Vdipole[0]+lambda_q*Vdipole[1]);
 620             }
 621         }
 622     }
 623 }
 624
 625 real ewald_charge_correction(t_commrec *cr, t_forcerec *fr, real lambda,
 626                              matrix box,
 627                              real *dvdlambda, tensor vir)
 628
 629 {
 630     real vol, fac, qs2A, qs2B, vc, enercorr;
 631     int  d;
 632
 633     if (MASTER(cr))
 634     {
 635         /* Apply charge correction */
 636         vol = box[XX][XX]*box[YY][YY]*box[ZZ][ZZ];
 637
 638         fac = M_PI*ONE_4PI_EPS0/(fr->epsilon_r*2.0*vol*vol*sqr(fr->ewaldcoeff_q));
 639
 640         qs2A = fr->qsum[0]*fr->qsum[0];
 641         qs2B = fr->qsum[1]*fr->qsum[1];
 642
 643         vc = (qs2A*(1 - lambda) + qs2B*lambda)*fac;
 644
 645         enercorr = -vol*vc;
 646
 647         *dvdlambda += -vol*(qs2B - qs2A)*fac;
 648
 649         for (d = 0; d < DIM; d++)
 650         {
 651             vir[d][d] += vc;
 652         }
 653
 654         if (debug)
 655         {
 656             fprintf(debug, "Total charge correction: Vcharge=%g\n", enercorr);
 657         }
 658     }
 659     else
 660     {
 661         enercorr = 0;
 662     }
 663
 664     return enercorr;
 665 }