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72 lines
2.8 KiB
Fortran
72 lines
2.8 KiB
Fortran
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subroutine example_becke_numerical_grid
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implicit none
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include 'constants.include.F'
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BEGIN_DOC
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! subroutine that illustrates the main features available in becke_numerical_grid
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END_DOC
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integer :: i,j,k,ipoint
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double precision :: integral_1, integral_2,alpha,center(3)
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print*,''
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print*,'**************'
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print*,'**************'
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print*,'routine that illustrates the use of the grid'
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print*,'**************'
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print*,'This grid is built as the reunion of a spherical grid around each atom'
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print*,'Each spherical grid contains a certain number of radial and angular points'
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print*,''
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print*,'n_points_integration_angular = ',n_points_integration_angular
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print*,'n_points_radial_grid = ',n_points_radial_grid
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print*,''
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print*,'As an example of the use of the grid, we will compute the integral of a 3D gaussian'
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! parameter of the gaussian: center of the gaussian is set to the first nucleus
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center(1:3)=nucl_coord(1,1:3)
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! alpha = exponent of the gaussian
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alpha = 1.d0
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print*,''
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print*,'The first example uses the grid points as one-dimensional array'
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print*,'This is the mostly used representation of the grid'
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print*,'It is the easyest way to use it with no drawback in terms of accuracy'
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integral_1 = 0.d0
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! you browse all the grid points as a one-dimensional array
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do i = 1, n_points_final_grid
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double precision :: weight, r(3)
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! you get x, y and z of the ith grid point
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r(1) = final_grid_points(1,i)
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r(2) = final_grid_points(2,i)
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r(3) = final_grid_points(3,i)
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weight = final_weight_at_r_vector(i)
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double precision :: distance, f_r
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! you compute the function to be integrated
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distance = dsqrt( (r(1) - center(1))**2 + (r(2) - center(2))**2 + (r(3) - center(3))**2 )
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f_r = dexp(-alpha * distance*distance)
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! you add the contribution of the grid point to the integral
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integral_1 += f_r * weight
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enddo
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print*,'integral_1 =',integral_1
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print*,'(pi/alpha)**1.5 =',(pi / alpha)**1.5
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print*,''
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print*,''
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print*,'The second example uses the grid points as a collection of spherical grids centered on each atom'
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print*,'This is mostly useful if one needs to split contributions between radial/angular/atomic of an integral'
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! you browse the nuclei
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do i = 1, nucl_num
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! you browse the radial points attached to each nucleus
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do j = 1, n_points_radial_grid
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! you browse the angular points attached to each radial point of each nucleus
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do k = 1, n_points_integration_angular
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r(1) = grid_points_per_atom(1,k,j,i)
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r(2) = grid_points_per_atom(2,k,j,i)
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r(3) = grid_points_per_atom(3,k,j,i)
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weight = final_weight_at_r(k,j,i)
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distance = dsqrt( (r(1) - center(1))**2 + (r(2) - center(2))**2 + (r(3) - center(3))**2 )
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f_r = dexp(-alpha * distance*distance)
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integral_2 += f_r * weight
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enddo
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enddo
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enddo
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print*,'integral_2 =',integral_2
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print*,'(pi/alpha)**1.5 =',(pi / alpha)**1.5
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print*,''
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end
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