From 57b47807fa1b7265345d877ca4902e87f39935ba Mon Sep 17 00:00:00 2001
From: Anthony Scemama <scemama@irsamc.ups-tlse.fr>
Date: Thu, 21 Apr 2022 14:25:29 +0200
Subject: [PATCH] Added CIS_read

---
 src/cis_read/EZFIO.cfg      |  7 +++
 src/cis_read/NEED           |  3 ++
 src/cis_read/README.rst     |  5 +++
 src/cis_read/cis_read.irp.f | 88 +++++++++++++++++++++++++++++++++++++
 src/cis_read/h_apply.irp.f  | 14 ++++++
 5 files changed, 117 insertions(+)
 create mode 100644 src/cis_read/EZFIO.cfg
 create mode 100644 src/cis_read/NEED
 create mode 100644 src/cis_read/README.rst
 create mode 100644 src/cis_read/cis_read.irp.f
 create mode 100644 src/cis_read/h_apply.irp.f

diff --git a/src/cis_read/EZFIO.cfg b/src/cis_read/EZFIO.cfg
new file mode 100644
index 00000000..955d1bef
--- /dev/null
+++ b/src/cis_read/EZFIO.cfg
@@ -0,0 +1,7 @@
+[energy]
+type: double precision
+doc: Variational |CIS| energy
+interface: ezfio
+size: (determinants.n_states)
+
+
diff --git a/src/cis_read/NEED b/src/cis_read/NEED
new file mode 100644
index 00000000..42992ac6
--- /dev/null
+++ b/src/cis_read/NEED
@@ -0,0 +1,3 @@
+selectors_full
+generators_full
+davidson_undressed
diff --git a/src/cis_read/README.rst b/src/cis_read/README.rst
new file mode 100644
index 00000000..31648636
--- /dev/null
+++ b/src/cis_read/README.rst
@@ -0,0 +1,5 @@
+===
+cis_read
+===
+
+Reads the input WF and performs all singles on top of it.
diff --git a/src/cis_read/cis_read.irp.f b/src/cis_read/cis_read.irp.f
new file mode 100644
index 00000000..055b5e15
--- /dev/null
+++ b/src/cis_read/cis_read.irp.f
@@ -0,0 +1,88 @@
+program cis
+  implicit none
+  BEGIN_DOC
+!
+! Configuration Interaction with Single excitations.
+!
+! This program takes a reference Slater determinant of ROHF-like
+! occupancy, and performs all single excitations on top of it.
+! Disregarding spatial symmetry, it computes the `n_states` lowest
+! eigenstates of that CI matrix. (see :option:`determinants n_states`)
+!
+! This program can be useful in many cases:
+!
+!
+! 1. Ground state calculation
+!
+!    To be sure to have the lowest |SCF| solution, perform an :ref:`scf`
+!    (see the :ref:`module_hartree_fock` module), then a :ref:`cis`, save the
+!    natural orbitals (see :ref:`save_natorb`) and re-run an :ref:`scf`
+!    optimization from this |MO| guess.
+!
+!
+! 2. Excited states calculations
+!
+!    The lowest excited states are much likely to be dominated by
+!    single-excitations. Therefore, running a :ref:`cis` will save the
+!    `n_states` lowest states within the |CIS| space in the |EZFIO|
+!    directory, which can afterwards be used as guess wave functions for
+!    a further multi-state |FCI| calculation if :option:`determinants
+!    read_wf` is set to |true| before running the :ref:`fci` executable.
+!
+!
+! If :option:`determinants s2_eig` is set to |true|, the |CIS|
+! will only retain states having the expected |S^2| value (see
+! :option:`determinants expected_s2`). Otherwise, the |CIS| will take
+! the lowest :option:`determinants n_states`, whatever multiplicity
+! they are.
+!
+! .. note::
+!
+!   To discard some orbitals, use the :ref:`qp_set_mo_class` 
+!   command to specify:
+!
+!   * *core* orbitals which will be always doubly occupied
+!
+!   * *act* orbitals where an electron can be either excited from or to
+!
+!   * *del* orbitals which will be never occupied
+!
+  END_DOC
+  read_wf = .True.
+  TOUCH read_wf
+  call run
+end
+
+subroutine run
+  implicit none
+  integer                        :: i
+
+
+  if(pseudo_sym)then
+   call H_apply_cis_sym
+  else
+   call H_apply_cis
+  endif
+  print*,''
+  print *,  'N_det = ', N_det
+  print*,'******************************'
+  print *,  'Energies  of the states:'
+  do i = 1,N_states
+    print *,  i, CI_energy(i)
+  enddo
+  if (N_states > 1) then
+    print*,''
+    print*,'******************************************************'
+    print*,'Excitation energies (au)                     (eV)'
+    do i = 2, N_states
+      print*, i ,CI_energy(i) - CI_energy(1), (CI_energy(i) - CI_energy(1))/0.0367502d0
+    enddo
+    print*,''
+  endif
+
+  call ezfio_set_cis_energy(CI_energy)
+  psi_coef = ci_eigenvectors
+  SOFT_TOUCH psi_coef
+  call save_wavefunction_truncated(save_threshold)
+
+end
diff --git a/src/cis_read/h_apply.irp.f b/src/cis_read/h_apply.irp.f
new file mode 100644
index 00000000..14389bed
--- /dev/null
+++ b/src/cis_read/h_apply.irp.f
@@ -0,0 +1,14 @@
+! Generates subroutine H_apply_cis
+! --------------------------------
+
+BEGIN_SHELL [ /usr/bin/env python3 ]
+from generate_h_apply import H_apply
+H = H_apply("cis",do_double_exc=False)
+print(H)
+
+H = H_apply("cis_sym",do_double_exc=False)
+H.filter_only_connected_to_hf()
+print(H)
+
+END_SHELL
+