From b39a7895f41c3c1297b041b52fca0af8d4de9a19 Mon Sep 17 00:00:00 2001
From: Kevin Gasperich <kgasperich@gmail.com>
Date: Mon, 3 Feb 2020 16:46:12 -0600
Subject: [PATCH] added kconserv array

---
 src/nuclei/EZFIO.cfg                     | 17 +++++++++++
 src/nuclei/kconserv_complex.irp.f        | 26 +++++++++++++++++
 src/utils_periodic/import_kconserv.irp.f | 36 ++++++++++++++++++++++++
 3 files changed, 79 insertions(+)
 create mode 100644 src/nuclei/kconserv_complex.irp.f
 create mode 100644 src/utils_periodic/import_kconserv.irp.f

diff --git a/src/nuclei/EZFIO.cfg b/src/nuclei/EZFIO.cfg
index 34c27c46..b95385f5 100644
--- a/src/nuclei/EZFIO.cfg
+++ b/src/nuclei/EZFIO.cfg
@@ -37,3 +37,20 @@ type: logical
 doc: If true, the calculation uses periodic boundary conditions
 interface: ezfio, provider, ocaml
 default: false
+
+[io_kconserv]
+doc: Read/Write kconserv array from/to disk [ Write | Read | None ]
+type: Disk_access
+interface: ezfio,provider,ocaml
+default: None
+
+[kpt_num]
+doc: Number of k-points
+type: integer
+interface: ezfio, provider
+
+[kconserv]
+type: integer
+doc: array containing information about k-point symmetry
+size: (nuclei.kpt_num,nuclei.kpt_num,nuclei.kpt_num)
+interface: ezfio
diff --git a/src/nuclei/kconserv_complex.irp.f b/src/nuclei/kconserv_complex.irp.f
new file mode 100644
index 00000000..11eb7daf
--- /dev/null
+++ b/src/nuclei/kconserv_complex.irp.f
@@ -0,0 +1,26 @@
+BEGIN_PROVIDER [integer, kconserv, (kpt_num,kpt_num,kpt_num)]
+  implicit none
+  BEGIN_DOC
+  ! Information about k-point symmetry
+  !
+  ! for k-points I,J,K: kconserv(I,J,K) gives L such that
+  ! k_I + k_J = k_K + k_L
+  ! two-electron integrals of the form <ij|kx>
+  ! (where i,j,k have momentum k_I, k_J, k_K)
+  ! will only be nonzero if x has momentum k_L (as described above)
+  !
+  END_DOC
+  integer                        :: i,j,k,l
+
+  if (read_kconserv) then
+    call ezfio_get_nuclei_kconserv(kconserv)
+    print *,  'kconserv read from disk'
+  else
+    print*,'kconserv must be provided'
+    stop -1
+  endif
+  if (write_kconserv) then
+    call ezfio_set_nuclei_kconserv(kconserv)
+    print *,  'kconserv written to disk'
+  endif
+END_PROVIDER
diff --git a/src/utils_periodic/import_kconserv.irp.f b/src/utils_periodic/import_kconserv.irp.f
new file mode 100644
index 00000000..0dff268b
--- /dev/null
+++ b/src/utils_periodic/import_kconserv.irp.f
@@ -0,0 +1,36 @@
+program import_kconserv
+
+  PROVIDE ezfio_filename
+  call run
+end
+
+subroutine run
+  use map_module
+  implicit none
+  BEGIN_DOC
+  ! read kconserv in physicists' notation order <ij|kl>
+  ! if kconserv(i,j,k)=l, then <ij|kl> is allowed by symmetry
+  ! NOTE: pyscf stores this internally in the order of chemists' notation (ik|jl)
+  END_DOC
+  
+  integer :: iunit
+  integer :: getunitandopen
+
+  integer ::i,j,k,l
+  integer, allocatable :: A(:,:,:)
+
+  allocate(A(kpt_num,kpt_num,kpt_num))
+  
+  A = 0
+  iunit = getunitandopen('kconserv','r')
+  do 
+    read (iunit,*,end=10) i,j,k,l
+    A(i,j,k) = l
+  enddo
+  10 continue
+  close(iunit)
+  call ezfio_set_nuclei_kconserv(A)
+  call ezfio_set_nuclei_io_kconserv("Read")
+  deallocate(A)
+
+end