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qp2/src/becke_numerical_grid/step_function_becke.irp.f
2019-03-27 13:14:55 +01:00

56 lines
2.1 KiB
Fortran

double precision function step_function_becke(x)
implicit none
BEGIN_DOC
! Step function of the Becke paper (1988, JCP,88(4))
END_DOC
double precision, intent(in) :: x
double precision :: f_function_becke
integer :: i,n_max_becke
step_function_becke = f_function_becke(x)
do i = 1, 4
step_function_becke = f_function_becke(step_function_becke)
enddo
step_function_becke = 0.5d0*(1.d0 - step_function_becke)
end
double precision function f_function_becke(x)
implicit none
double precision, intent(in) :: x
f_function_becke = 1.5d0 * x - 0.5d0 * x*x*x
end
double precision function cell_function_becke(r,atom_number)
implicit none
double precision, intent(in) :: r(3)
integer, intent(in) :: atom_number
BEGIN_DOC
! atom_number :: atom on which the cell function of Becke (1988, JCP,88(4))
! r(1:3) :: x,y,z coordinantes of the current point
END_DOC
double precision :: mu_ij,nu_ij
double precision :: distance_i,distance_j,step_function_becke
integer :: j
if(int(nucl_charge(atom_number))==0)then
cell_function_becke = 0.d0
return
endif
distance_i = (r(1) - nucl_coord_transp(1,atom_number) ) * (r(1) - nucl_coord_transp(1,atom_number))
distance_i += (r(2) - nucl_coord_transp(2,atom_number) ) * (r(2) - nucl_coord_transp(2,atom_number))
distance_i += (r(3) - nucl_coord_transp(3,atom_number) ) * (r(3) - nucl_coord_transp(3,atom_number))
distance_i = dsqrt(distance_i)
cell_function_becke = 1.d0
do j = 1, nucl_num
if(j==atom_number)cycle
if(int(nucl_charge(j))==0)cycle
distance_j = (r(1) - nucl_coord_transp(1,j) ) * (r(1) - nucl_coord_transp(1,j))
distance_j+= (r(2) - nucl_coord_transp(2,j) ) * (r(2) - nucl_coord_transp(2,j))
distance_j+= (r(3) - nucl_coord_transp(3,j) ) * (r(3) - nucl_coord_transp(3,j))
distance_j = dsqrt(distance_j)
mu_ij = (distance_i - distance_j)*nucl_dist_inv(atom_number,j)
nu_ij = mu_ij + slater_bragg_type_inter_distance_ua(atom_number,j) * (1.d0 - mu_ij*mu_ij)
cell_function_becke *= step_function_becke(nu_ij)
enddo
end