matelt_CF_Hamil.f90_FR_Phase_System

!***********************************************************************
!                                                                      *
      SUBROUTINE MATELT_CF_Hamil (K,I1,I2,APART)
!                                                                      *
!     This routine computes the angular part of the reduced matrix     *
!     elements of the crystal field operator.                          *
!                                                                      *
!     Written by G. Gaigalas and D. Kato                               *
!                                        NIFS, Japan, September 2013   *
!     The last modification made by G. Gaigalas       June      2018   *
!                                                                      *
!***********************************************************************
!-----------------------------------------------
!   M o d u l e s
!-----------------------------------------------
      USE vast_kind_param, ONLY: DOUBLE
      USE CONS_C,          ONLY: ZERO
      USE parameter_def,   ONLY: NNNW
      USE orb_C,           ONLY: NAK
      IMPLICIT NONE
!-----------------------------------------------
!   I n t e r f a c e   B l o c k s
!-----------------------------------------------
      USE CLRX_I
!-----------------------------------------------
!   D u m m y   A r g u m e n t s
!-----------------------------------------------
      INTEGER, INTENT(IN)       :: K, I1, I2
      REAL(DOUBLE), INTENT(OUT) :: APART
!-----------------------------------------------
!   L o c a l   V a r i a b l e s
!-----------------------------------------------
      INTEGER      :: KAP1, KAP2, L1, L2
      REAL(DOUBLE) :: FASE, OVLFAC
!-----------------------------------------------
!
!   Set KAP1 and KAP2
!
      KAP1 = NAK(I1)
      KAP2 = NAK(I2)
!
!   Determine the l quantum numbers
!
      IF (KAP1 > 0) THEN
         L1 =  KAP1
      ELSE
         L1 = -KAP1-1
      ENDIF
!
      IF (KAP2 > 0) THEN
         L2 =  KAP2
      ELSE
         L2 = -KAP2-1
      ENDIF
!
      IF (MOD (L1+K+L2,2) == 0) THEN
!
!   Parity selection rule satisfied
!
!   Determine the phase factor
!
!GG         IF (MOD (KAP1+1,2) == 0) THEN
         IF (MOD (IABS(KAP1),2) == 0) THEN
            FASE =  1.0D 00
         ELSE
            FASE = -1.0D 00
         ENDIF
!
!   The other factor is \sqrt (2 j_2 + 1); since j = | \kappa | - 1/2,
!   we have 2 j_2 + 1 = 2 | \kappa |; the factor \sqrt (2 j_2 + 1)
!   has been accounted for in MCT
!
         OVLFAC = FASE * SQRT (DBLE (2*ABS (KAP2)))
!GG         OVLFAC = FASE * SQRT (DBLE (4*ABS (KAP1)*ABS (KAP2)))
!GG         OVLFAC = FASE *SQRT (DBLE (8*ABS (KAP1)*ABS (KAP1)*ABS (KAP2)))
!
         APART =   CLRX (KAP1,K,KAP2) * OVLFAC
      ELSE
         APART = ZERO
      ENDIF
!GG V9      IF (MOD (L2-L1,4) /= 0) APART = -APART
      IF (MOD (L2-K-L1,4) /= 0) APART = -APART
!GG      IF (MOD (L2-2*K-L1,4) /= 0) APART = -APART
!
      RETURN
      END SUBROUTINE MATELT_CF_Hamil