C
C $Id: boxstep.F,v 1.6 1998/07/16 16:39:26 jjv5 Exp arjan $
C
C------------------------------------------------------------------------
      subroutine boxstep(ok)

C
C     acceptance / rejection criteria after boxmove
C*****NOTE: this version assumes that every molecule is a residue!
C
      implicit double precision (a-h,o-z)
#include "divcon.dim"
#include "divcon.h"

      logical ok

CCC------------------------------------------------------CCC


      ok = .false.

C     calculate deltaH = deltaE + P*deltaV - N*beta^(-1)*ln(Vnew/Vold)
C     note that N (=number of molecules) is assumed to be nres.

      pterm = press*boxvol - (dble(nres)*log(boxvol))/boltzt
      enth = etot + pterm
      delta = (enth-enthmc)*boltzt
      ntry = ntry + 1
      if (delta .lt. 75.) then
         if (delta .le. 0.0) then
C           accept, because etot < etotmc
C           calculate the new grid
            ok = .true.
         elseif (exp(-delta) .gt. xrandom(iseed)) then
C           accept, MC
            ok = .true.
         endif
      endif



      end