Examples

Accessing sparse quantities
- Fortran

Accessing sparse quantities

Fortran

program print_energy
use trexio
implicit none

character*(128)  :: filename   ! Name of the input file
integer          :: rc         ! Return code for error checking
integer(8)       :: f          ! TREXIO file handle
character*(128)  :: err_msg    ! Error message

This program computes the energy as:

\[ E = E_{\text{NN}} + \sum_{ij} D_{ij}\, \langle i | h | j \rangle\, +\, \frac{1}{2} \sum_{ijkl} \Gamma_{ijkl}\, \langle i j | k l \rangle\; \textrm{ with } \; 0 < i,j,k,l \le n \]

One needs to read from the TREXIO file:

$n$: The number of molecular orbitals
$E_{\text{NN}}$: The nuclear repulsion energy
$D_{ij}$: The one-body reduced density matrix
$\langle i |h| j \rangle$: The one-electron Hamiltonian integrals
$\Gamma_{ijkl}$: The two-body reduced density matrix
$\langle i j | k l \rangle$: The electron repulsion integrals

integer                       :: n
double precision              :: E, E_nn
double precision, allocatable :: D(:,:), h0(:,:)
double precision, allocatable :: G(:,:,:,:), W(:,:,:,:)

Declare Temporary variables

integer                       :: i, j, k, l, m
integer(8), parameter         :: BUFSIZE = 10000_8
integer(8)                    :: offset, icount, size_max
integer                       :: buffer_index(4,BUFSIZE)
double precision              :: buffer_values(BUFSIZE)

double precision, external    :: ddot   ! BLAS dot product

Obtain the name of the TREXIO file from the command line, and open it for reading

call getarg(1, filename)

f = trexio_open (filename, 'r', TREXIO_HDF5, rc)
if (rc /= TREXIO_SUCCESS) then
  call trexio_string_of_error(rc, err_msg)
  print *, 'Error opening TREXIO file: '//trim(err_msg)
  stop
end if

Read the nuclear repulsion energy

rc = trexio_read_nucleus_repulsion(f, E_nn)
if (rc /= TREXIO_SUCCESS) then
  call trexio_string_of_error(rc, err_msg)
  print *, 'Error reading nuclear repulsion: '//trim(err_msg)
  stop
end if

Read the number of molecular orbitals

rc = trexio_read_mo_num(f, n)
if (rc /= TREXIO_SUCCESS) then
 call trexio_string_of_error(rc, err_msg)
 print *, 'Error reading number of MOs: '//trim(err_msg)
 stop
end if

Allocate memory

allocate( D(n,n), h0(n,n) )
allocate( G(n,n,n,n), W(n,n,n,n) )

Read one-electron quantities

rc = trexio_has_mo_1e_int_core_hamiltonian(f)
if (rc /= TREXIO_SUCCESS) then
 stop 'No core hamiltonian in file'
end if

rc = trexio_read_mo_1e_int_core_hamiltonian(f, h0)
if (rc /= TREXIO_SUCCESS) then
 call trexio_string_of_error(rc, err_msg)
 print *, 'Error reading core Hamiltonian: '//trim(err_msg)
 stop
end if


rc = trexio_has_rdm_1e(f)
if (rc /= TREXIO_SUCCESS) then
 stop 'No 1e RDM in file'
end if

rc = trexio_read_rdm_1e(f, D)
if (rc /= TREXIO_SUCCESS) then
 call trexio_string_of_error(rc, err_msg)
 print *, 'Error reading one-body RDM: '//trim(err_msg)
 stop
end if

Read two-electron quantities

rc = trexio_has_mo_2e_int_eri(f)
if (rc /= TREXIO_SUCCESS) then
 stop 'No electron repulsion integrals in file'
end if

rc = trexio_read_mo_2e_int_eri_size (f, size_max)
if (rc /= TREXIO_SUCCESS) then
 call trexio_string_of_error(rc, err_msg)
 print *, 'Error reading number of ERIs: '//trim(err_msg)
 stop
end if

W(:,:,:,:) = 0.d0
icount = BUFSIZE
offset = 0_8
do while (offset < size_max)
rc = trexio_read_mo_2e_int_eri(f, offset, icount, buffer_index, buffer_values)
if (rc /= TREXIO_SUCCESS) exit
do m=1,min(icount, size_max-offset)
  i = buffer_index(1,m)
  j = buffer_index(2,m)
  k = buffer_index(3,m)
  l = buffer_index(4,m)
  W(i,j,k,l) = buffer_values(m)
  W(k,j,i,l) = buffer_values(m)
  W(i,l,k,j) = buffer_values(m)
  W(k,l,i,j) = buffer_values(m)
  W(j,i,l,k) = buffer_values(m)
  W(j,k,l,i) = buffer_values(m)
  W(l,i,j,k) = buffer_values(m)
  W(l,k,j,i) = buffer_values(m)
end do
offset = offset + icount
end do


rc = trexio_has_rdm_2e(f)
if (rc /= TREXIO_SUCCESS) then
 stop 'No two-body density matrix in file'
end if

rc = trexio_read_rdm_2e_size (f, size_max)
if (rc /= TREXIO_SUCCESS) then
 call trexio_string_of_error(rc, err_msg)
 print *, 'Error reading number of 2-RDM elements: '//trim(err_msg)
 stop
end if

G(:,:,:,:) = 0.d0
icount = BUFSIZE
offset = 0_8
do while (offset < size_max)
rc = trexio_read_rdm_2e(f, offset, icount, buffer_index, buffer_values)
if (rc /= TREXIO_SUCCESS) exit
do m=1,min(icount, size_max-offset)
  i = buffer_index(1,m)
  j = buffer_index(2,m)
  k = buffer_index(3,m)
  l = buffer_index(4,m)
  G(i,j,k,l) = buffer_values(m)
end do
offset = offset + icount
end do

Compute the energy

E =  E_nn +                           &
   ddot( n**2, D, 1, h0, 1 ) + &
   0.5d0 * ddot( n**4, G, 1, W,  1 )

print *, 'Energy: ', E

Terminate

deallocate( D, h0, G, W )

end program

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