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Better documentation in examples
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examples.org
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examples.org
@ -48,7 +48,7 @@ program print_energy
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#+begin_src f90
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integer :: i, j, k, l, m
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integer(8), parameter :: BUFSIZE = 10000_8
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integer(8), parameter :: BUFSIZE = 100000_8
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integer(8) :: offset, icount, size_max
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integer :: buffer_index(4,BUFSIZE)
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double precision :: buffer_values(BUFSIZE)
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@ -96,6 +96,8 @@ program print_energy
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#+begin_src f90
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allocate( D(n,n), h0(n,n) )
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allocate( G(n,n,n,n), W(n,n,n,n) )
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G(:,:,:,:) = 0.d0
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W(:,:,:,:) = 0.d0
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#+end_src
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*** Read one-electron quantities
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@ -129,12 +131,23 @@ program print_energy
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*** Read two-electron quantities
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#+begin_src f90
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Reading is done with OpenMP. Each thread reads its own buffer, and
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the buffers are then processed in parallel.
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Reading the file requires a lock, so it is done in a critical
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section. The ~offset~ variable is shared, and it is incremented in
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the critical section. For each read, the function returns in
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~icount~ the number of read integrals, so this variable needs also
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to be protected in the critical section when modified.
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**** Electron repulsion integrals
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#+begin_src f90
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rc = trexio_has_mo_2e_int_eri(f)
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if (rc /= TREXIO_SUCCESS) then
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stop 'No electron repulsion integrals in file'
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end if
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rc = trexio_read_mo_2e_int_eri_size (f, size_max)
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if (rc /= TREXIO_SUCCESS) then
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call trexio_string_of_error(rc, err_msg)
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@ -142,13 +155,20 @@ program print_energy
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stop
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end if
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W(:,:,:,:) = 0.d0
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icount = BUFSIZE
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offset = 0_8
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do while (offset < size_max)
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rc = trexio_read_mo_2e_int_eri(f, offset, icount, buffer_index, buffer_values)
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if (rc /= TREXIO_SUCCESS) exit
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do m=1,min(icount, size_max-offset)
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!$OMP PARALLEL DEFAULT(SHARED) PRIVATE(icount, i, j, k, l, &
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!$OMP buffer_index, buffer_values, m)
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icount = BUFSIZE
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do while (icount == BUFSIZE)
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!$OMP CRITICAL
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if (offset < size_max) then
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rc = trexio_read_mo_2e_int_eri(f, offset, icount, buffer_index, buffer_values)
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offset = offset + icount
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else
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icount = 0
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end if
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!$OMP END CRITICAL
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do m=1,icount
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i = buffer_index(1,m)
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j = buffer_index(2,m)
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k = buffer_index(3,m)
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@ -162,10 +182,13 @@ program print_energy
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W(l,i,j,k) = buffer_values(m)
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W(l,k,j,i) = buffer_values(m)
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end do
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offset = offset + icount
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end do
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!$OMP END PARALLEL
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#+end_src
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**** Reduced density matrix
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#+begin_src f90
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rc = trexio_has_rdm_2e(f)
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if (rc /= TREXIO_SUCCESS) then
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stop 'No two-body density matrix in file'
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@ -178,30 +201,54 @@ program print_energy
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stop
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end if
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G(:,:,:,:) = 0.d0
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icount = BUFSIZE
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offset = 0_8
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!$OMP PARALLEL DEFAULT(SHARED) PRIVATE(icount, i, j, k, l, &
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!$OMP buffer_index, buffer_values, m)
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icount = bufsize
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do while (offset < size_max)
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rc = trexio_read_rdm_2e(f, offset, icount, buffer_index, buffer_values)
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if (rc /= TREXIO_SUCCESS) exit
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do m=1,min(icount, size_max-offset)
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!$OMP CRITICAL
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if (offset < size_max) then
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rc = trexio_read_rdm_2e(f, offset, icount, buffer_index, buffer_values)
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offset = offset + icount
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else
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icount = 0
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end if
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!$OMP END CRITICAL
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do m=1,icount
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i = buffer_index(1,m)
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j = buffer_index(2,m)
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k = buffer_index(3,m)
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l = buffer_index(4,m)
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G(i,j,k,l) = buffer_values(m)
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end do
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offset = offset + icount
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end do
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#+end_src
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!$OMP END PARALLEL
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#+end_src
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*** Compute the energy
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As $(n,m)$ 2D arrays are stored in memory as $(\n times m)$ 1D
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arrays, we could pass the matrices to the ~ddot~ BLAS function to
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perform the summations in a single call for the 1-electron quantities.
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Instead, we prefer to interleave the 1-electron (negative) and
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2-electron (positive) summations to have a better cancellation of
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numerical errors.
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Here $n^4$ can be larger than the largest possible 32-bit integer,
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so it is not safe to pass $n^4$ to the ~ddot~ BLAS
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function. Hence, we perform $n^2$ loops, using vectors of size $n^2$.
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#+begin_src f90
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E = E_nn + &
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ddot( n**2, D, 1, h0, 1 ) + &
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0.5d0 * ddot( n**4, G, 1, W, 1 )
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E = 0.d0
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do l=1,n
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E = E + ddot( n, D(1,l), 1, h0(1,l), 1 )
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do k=1,n
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E = E + 0.5d0 * ddot( n*n, G(1,1,k,l), 1, W(1,1,k,l), 1 )
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end do
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end do
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E = E + E_nn
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print *, 'Energy: ', E
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#+end_src
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