2014-05-13 13:57:58 +02:00
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subroutine get_s2(key_i,key_j,phase,Nint)
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implicit none
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2014-05-19 18:35:56 +02:00
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use bitmasks
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2014-05-13 13:57:58 +02:00
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BEGIN_DOC
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! Returns <S^2>
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END_DOC
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integer, intent(in) :: Nint
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2014-05-19 18:35:56 +02:00
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integer(bit_kind), intent(in) :: key_i(Nint,2)
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integer(bit_kind), intent(in) :: key_j(Nint,2)
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2014-05-13 13:57:58 +02:00
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double precision, intent(out) :: phase
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integer :: exc(0:2,2,2)
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integer :: degree
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double precision :: phase_spsm
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integer :: nup, i
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phase = 0.d0
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!$FORCEINLINE
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call get_excitation_degree(key_i,key_j,degree,Nint)
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select case (degree)
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case(2)
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call get_double_excitation(key_i,key_j,exc,phase_spsm,Nint)
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if (exc(0,1,1) == 1) then ! Mono alpha + mono-beta
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if ( (exc(1,1,1) == exc(1,2,2)).and.(exc(1,1,2) == exc(1,2,1)) ) then
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phase = -phase_spsm
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endif
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endif
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case(0)
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nup = 0
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do i=1,Nint
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nup += popcnt(iand(xor(key_i(i,1),key_i(i,2)),key_i(i,1)))
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enddo
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phase = dble(nup)
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end select
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end
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2014-05-19 18:35:56 +02:00
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BEGIN_PROVIDER [ double precision, S_z ]
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&BEGIN_PROVIDER [ double precision, S_z2_Sz ]
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implicit none
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S_z = 0.5d0*dble(elec_alpha_num-elec_beta_num)
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S_z2_Sz = S_z*(S_z-1.d0)
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END_PROVIDER
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subroutine get_s2_u0(psi_keys_tmp,psi_coefs_tmp,n,nmax,s2)
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implicit none
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use bitmasks
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integer(bit_kind), intent(in) :: psi_keys_tmp(N_int,2,nmax)
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integer, intent(in) :: n,nmax
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double precision, intent(in) :: psi_coefs_tmp(nmax)
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double precision, intent(out) :: s2
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integer :: i,j,l
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double precision :: s2_tmp
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s2 = S_z2_Sz
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!$OMP PARALLEL DO DEFAULT(NONE) &
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!$OMP PRIVATE(i,j,s2_tmp) SHARED(n,psi_coefs_tmp,psi_keys_tmp,N_int) &
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!$OMP REDUCTION(+:s2) SCHEDULE(dynamic)
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do i = 1, n
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call get_s2(psi_keys_tmp(1,1,i),psi_keys_tmp(1,1,i),s2_tmp,N_int)
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! print*,'s2_tmp = ',s2_tmp
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do j = 1, n
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call get_s2(psi_keys_tmp(1,1,i),psi_keys_tmp(1,1,j),s2_tmp,N_int)
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if (s2_tmp == 0.d0) cycle
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s2 += psi_coefs_tmp(i)*psi_coefs_tmp(j)*s2_tmp
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enddo
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enddo
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!$OMP END PARALLEL DO
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end
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