Chimie Théorique » OpenPath

subroutine cmshft(natom,rx,ry,rz,rmass,cmx,cmy,cmz,ishift)

  !c

  !c      shifts all x, y, and z coordinates passed in rx,ry,rz to keep

  !c      the center of mass at the origin if ishift is not zero. otherwise

  !c      cmx, cmy, and cmz return the center of mass coordinates and no

  !c      shift is performed. coordinate and mass units arbitrary.

  !c

  use VarTypes

  use Io_module

  IMPLICIT NONE

! Number of atoms

  INTEGER(KINT), INTENT(IN) :: NAtom

! Coordinates and masses 

  REAL(KREAL), DIMENSION(NAtom) :: rx,ry,rz,rmass

! Center of mass coordinates

  real(KREAL) :: cmx,cmy,cmz

! Flag if user wants to shift center of mass to origin

  INTEGER(KINT) :: IShift

  REAL(KREAL), parameter :: zero=0.d0,one=1.d0

  INTEGER(KINT) :: i,j

  REAL(KREAL) :: TmassI, tmass

  if(natom.le.0) then

     if(IOOUT.gt.0) write(IOOUT,'(/2a/)')  &

          '  *** error, illegal array dimension in cmshft,', &

          ' return without action ***'

     return

  end if

  !c

  !c      calculate center of mass coordinates

  !c

  tmass=rmass(1)

  do j=2,natom

     tmass=tmass+rmass(j)

  END DO

  !c

  !c     DO i=1,natom

  !c       write(IOOUT,'(4F15.3)') rmass(i),rx(i),ry(i),rz(i)

  !c     END DO

  cmx=zero

  cmy=zero

  cmz=zero

  do j=1,natom

     cmx=rmass(j)*rx(j)+cmx

     cmy=rmass(j)*ry(j)+cmy

     cmz=rmass(j)*rz(j)+cmz

  END DO

  tmassi=one/tmass

  cmx=cmx*tmassi

  cmy=cmy*tmassi

  cmz=cmz*tmassi

  !c

  !c      optional shift of all cartesian coordinates

  !c

  if(ishift.ne.0) then

     do j=1,natom

        rx(j)=rx(j)-cmx

        ry(j)=ry(j)-cmy

        rz(j)=rz(j)-cmz

     END DO

  end if

  return

end subroutine cmshft