# sltcnd_1_base_ua Function

## private function sltcnd_1_base_ua(nI, ex, tSign, assert_occupation) result(hel)

### Arguments

Type IntentOptional Attributes Name
integer, intent(in) :: nI(nel)
type(Excite_1_t), intent(in) :: ex
logical, intent(in) :: tSign
logical, intent(in), optional :: assert_occupation

## Source Code

    function sltcnd_1_base_ua(nI, ex, tSign, assert_occupation) result(hel)
! Calculate the  by the Slater-Condon Rules when the two
! determinants differ by one orbital exactly.
integer, intent(in) :: nI(nel)
type(Excite_1_t), intent(in) :: ex
logical, intent(in) :: tSign
logical, intent(in), optional :: assert_occupation
HElement_t(dp) :: hel
debug_function_name("sltcnd_1_base_ua")
#ifdef DEBUG_
block
use constants, only: stderr
use util_mod, only: stop_all
logical :: test_occupation

if (present(assert_occupation)) then
test_occupation = assert_occupation
else
test_occupation = .true.
end if

if (test_occupation) then
if (.not. occupation_allowed(nI, ex)) then
write(stderr, *) 'src', ex%val(1, :)
write(stderr, *) 'tgt', ex%val(2, :)
write(stderr, *) 'nI', nI
call stop_all(this_routine, "Not allowed by occupation.")
end if
end if
end block
#endif

! Sum in the diagonal terms (same in both dets)
! Coulomb term only included if Ms values of ex(1) and ex(2) are the
! same.

hel = sltcnd_1_kernel_ua(nI, ex)
if (tSign) hel = -hel
end function sltcnd_1_base_ua