get_atomic_c6 Subroutine

subroutine get_atomic_c6(self, mol, gwvec, gwdcn, gwdq, c6, dc6dcn, dc6dq)
   !DEC$ ATTRIBUTES DLLEXPORT :: get_atomic_c6

   !> Instance of the dispersion model
   class(d4_model), intent(in) :: self

   !> Molecular structure data
   class(structure_type), intent(in) :: mol

   !> Weighting function for the atomic reference systems
   real(wp), intent(in) :: gwvec(:, :)

   !> Derivative of the weighting function w.r.t. the coordination number
   real(wp), intent(in), optional :: gwdcn(:, :)

   !> Derivative of the weighting function w.r.t. the partial charge
   real(wp), intent(in), optional :: gwdq(:, :)

   !> C6 coefficients for all atom pairs.
   real(wp), intent(out) :: c6(:, :)

   !> Derivative of the C6 w.r.t. the coordination number
   real(wp), intent(out), optional :: dc6dcn(:, :)

   !> Derivative of the C6 w.r.t. the partial charge
   real(wp), intent(out), optional :: dc6dq(:, :)

   integer :: iat, jat, izp, jzp, iref, jref
   real(wp) :: refc6, dc6, dc6dcni, dc6dcnj, dc6dqi, dc6dqj

   if (present(gwdcn).and.present(dc6dcn) &
      & .and.present(gwdq).and.present(dc6dq)) then
      c6(:, :) = 0.0_wp
      dc6dcn(:, :) = 0.0_wp
      dc6dq(:, :) = 0.0_wp

      !$omp parallel do default(none) schedule(runtime) &
      !$omp shared(c6, dc6dcn, dc6dq, mol, self, gwvec, gwdcn, gwdq) &
      !$omp private(iat, jat, izp, jzp, iref, jref, refc6, dc6, dc6dqi, dc6dqj, &
      !$omp& dc6dcni, dc6dcnj)
      do iat = 1, mol%nat
         izp = mol%id(iat)
         do jat = 1, iat
            jzp = mol%id(jat)
            dc6 = 0.0_wp
            dc6dcni = 0.0_wp
            dc6dcnj = 0.0_wp
            dc6dqi = 0.0_wp
            dc6dqj = 0.0_wp
            do iref = 1, self%ref(izp)
               do jref = 1, self%ref(jzp)
                  refc6 = self%c6(iref, jref, izp, jzp)
                  dc6 = dc6 + gwvec(iref, iat) * gwvec(jref, jat) * refc6
                  dc6dcni = dc6dcni + gwdcn(iref, iat) * gwvec(jref, jat) * refc6
                  dc6dcnj = dc6dcnj + gwvec(iref, iat) * gwdcn(jref, jat) * refc6
                  dc6dqi = dc6dqi + gwdq(iref, iat) * gwvec(jref, jat) * refc6
                  dc6dqj = dc6dqj + gwvec(iref, iat) * gwdq(jref, jat) * refc6
               end do
            end do
            c6(iat, jat) = dc6
            c6(jat, iat) = dc6
            dc6dcn(iat, jat) = dc6dcni
            dc6dcn(jat, iat) = dc6dcnj
            dc6dq(iat, jat) = dc6dqi
            dc6dq(jat, iat) = dc6dqj
         end do
      end do

   else

      c6(:, :) = 0.0_wp

      !$omp parallel do default(none) schedule(runtime) &
      !$omp shared(c6, mol, self, gwvec) &
      !$omp private(iat, jat, izp, jzp, iref, jref, refc6, dc6)
      do iat = 1, mol%nat
         izp = mol%id(iat)
         do jat = 1, iat
            jzp = mol%id(jat)
            dc6 = 0.0_wp
            do iref = 1, self%ref(izp)
               do jref = 1, self%ref(jzp)
                  refc6 = self%c6(iref, jref, izp, jzp)
                  dc6 = dc6 + gwvec(iref, iat) * gwvec(jref, jat) * refc6
               end do
            end do
            c6(iat, jat) = dc6
            c6(jat, iat) = dc6
         end do
      end do
   end if

end subroutine get_atomic_c6