[gmx-users] ewald_util.c, charge and dipole corrections

[Y U Sasidhar]

I am attaching below code fragment from ewals_util.c. The 
code refers to charge and dipole corrections. What are these 
corrections ? I will be thankful to you for your response.

/* Global corrections only on master process */
   if(MASTER(cr)) {
     /* Apply charge correction */
     /* use vc as a dummy variable */
     vc=qsum*qsum*M_PI*ONE_4PI_EPS0/(2.0*vol*vol*ewc*ewc);
     for(iv=0;iv<DIM;iv++)
       lr_vir[iv][iv]+=vc;
     Vcharge=-vol*vc;

     /* Apply surface dipole correction:
      * correction = dipole_coeff * (dipole)^2
      * Note that we have to transform back to gromacs 
units, since
      * mu_tot contains the dipole in debye units (for output).
      */
     if(dipole_coeff!=0) {
       if(ewald_geometry==eewg3D)
	Vdipole=dipole_coeff*DEBYE2ENM*DEBYE2ENM*
	 
(mu_tot[XX]*mu_tot[XX]+mu_tot[YY]*mu_tot[YY]+mu_tot[ZZ]*mu_tot[ZZ]);
       else if(ewald_geometry==eewg3DC)
	Vdipole=dipole_coeff*DEBYE2ENM*DEBYE2ENM*mu_tot[ZZ]*mu_tot[ZZ];
     }
   }
-- 
  Sasidhar