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68 lines
2.1 KiB
Fortran
68 lines
2.1 KiB
Fortran
subroutine do_mono_excitation(key_in,i_hole,i_particle,ispin,i_ok)
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implicit none
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BEGIN_DOC
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! Apply the single excitation operator : a^{dager}_(i_particle) a_(i_hole) of spin = ispin
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! on key_in
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! ispin = 1 == alpha
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! ispin = 2 == beta
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! i_ok = 1 == the excitation is possible
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! i_ok = -1 == the excitation is not possible
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END_DOC
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integer, intent(in) :: i_hole,i_particle,ispin
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integer(bit_kind), intent(inout) :: key_in(N_int,2)
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integer, intent(out) :: i_ok
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integer :: k,j,i
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use bitmasks
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ASSERT (i_hole > 0 )
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ASSERT (i_particle <= mo_num)
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i_ok = 1
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! hole
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k = shiftr(i_hole-1,bit_kind_shift)+1
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j = i_hole-shiftl(k-1,bit_kind_shift)-1
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key_in(k,ispin) = ibclr(key_in(k,ispin),j)
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! particle
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k = shiftr(i_particle-1,bit_kind_shift)+1
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j = i_particle-shiftl(k-1,bit_kind_shift)-1
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key_in(k,ispin) = ibset(key_in(k,ispin),j)
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integer :: n_elec_tmp
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n_elec_tmp = 0
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do i = 1, N_int
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n_elec_tmp += popcnt(key_in(i,1)) + popcnt(key_in(i,2))
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enddo
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if(n_elec_tmp .ne. elec_num)then
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!print*, n_elec_tmp,elec_num
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!call debug_det(key_in,N_int)
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i_ok = -1
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endif
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end
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logical function is_spin_flip_possible(key_in,i_flip,ispin)
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implicit none
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BEGIN_DOC
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! returns |true| if the spin-flip of spin ispin in the orbital i_flip is possible
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! on key_in
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END_DOC
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integer, intent(in) :: i_flip,ispin
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integer(bit_kind), intent(in) :: key_in(N_int,2)
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integer :: k,j,i
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integer(bit_kind) :: key_tmp(N_int,2)
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is_spin_flip_possible = .False.
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key_tmp = 0_bit_kind
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k = shiftr(i_flip-1,bit_kind_shift)+1
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j = i_flip-shiftl(k-1,bit_kind_shift)-1
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key_tmp(k,1) = ibset(key_tmp(k,1),j)
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integer :: other_spin(2)
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other_spin(1) = 2
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other_spin(2) = 1
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if(popcnt(iand(key_tmp(k,1),key_in(k,ispin))) == 1 .and. popcnt(iand(key_tmp(k,1),key_in(k,other_spin(ispin)))) == 0 )then
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! There is a spin "ispin" in the orbital i_flip AND There is no electron of opposit spin in the same orbital "i_flip"
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is_spin_flip_possible = .True.
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return
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else
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return
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endif
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end
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