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  SUBROUTINE egrad_test(nat,e,geom,grad) 
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! This program reads cartesian coordinates from the file Ext.in
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! and print the energy (in au) and gradient (in au/Ang) in the file Ext.out
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! format D25.15
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   IMPLICIT NONE
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     integer, parameter :: KINT = kind(1)
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     integer, parameter :: KREAL = kind(1.0d0)
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       INTEGER(KINT), INTENT(IN) :: Nat
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       REAL(KREAL), INTENT(OUT) :: E,grad(Nat*3)
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       REAL(KREAL), INTENT(IN) :: Geom(Nat,3)
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!     Bohr --> Angstr
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      real(KREAL), parameter :: BOHR   = 0.52917726D+00
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!
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! Parameters to define the surface
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      INTEGER(KINT), DIMENSION(6), PARAMETER :: IECOEF = (/-1,9,-45,45,-9,1/)
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      INTEGER(KINT), DIMENSION(6), PARAMETER :: ISCOEF = (/-3,-2,-1,1,2,3/)
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      REAL(KREAL), PARAMETER :: hh=0.001d0
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! Variables
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       INTEGER(KINT) :: i,j,iat,jat
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       REAL(KREAL), ALLOCATABLE :: Xyztmp(:,:),GradTmp(:,:)
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       REAL(KREAL) :: xp,yp
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       CHARACTER(132) :: Line
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       LOGICAL :: Debug
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      real(KREAL), parameter :: zero = 0.0_KREAL,   one = 1.0_KREAL
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      REAL(KREAL), external :: Exyz 
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  INTERFACE
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     function valid(string) result (isValid)
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       CHARACTER(*), intent(in) :: string
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       logical                  :: isValid
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     END function VALID
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  END INTERFACE
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  debug=valid('egrad_test')
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 if (debug) WRITE(*,*) '================ Entering Egrad_test ==================='
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 if (debug) THEN
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    WRITE(*,*) "Cartesian Geometry"
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    DO I=1,Nat
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       WRITE(*,'(1X,I5,3(1X,F12.6))') I,Geom(i,1:3)
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    END DO
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 END IF
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      ALLOCATE(XyZTmp(Nat,3),GradTmp(Nat,3))
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      e=Exyz(nat,Geom)
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! We now calculate the gradients using numerical derivatives
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      Grad=0.d0
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      GradTmp=0.d0
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      do iat=1,3
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         do jat=1,nat
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            xyztmp=geom
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            do i=1,6
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               xyztmp(jat,iat)=geom(jat,iat)+ISCoef(i)*hh
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               gradTmp(jat,iat)=gradTmp(jat,iat)+IECoef(i)*Exyz(nat,xyztmp)
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            end do
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         end do
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      end do
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      gradTmp=gradTmp/(60.*hh)
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      do iat=1,nat
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       grad(3*iat-2:3*iat)=gradTmp(iat,1:3)
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      end do
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 if (debug) THEN
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    WRITE(*,*) "Cartesian gradient GradTmp"
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    DO I=1,Nat
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       WRITE(*,'(1X,I5,3(1X,F12.6))') I,Gradtmp(i,1:3)
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    END DO
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    WRITE(*,*) "Cartesian gradient Grad"
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    WRITE(*,'(50(1X,F12.6))') Grad
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 END IF
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      deallocate(xyztmp,gradTmp)
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 if (debug) WRITE(*,*) '================ Exiting Egrad_test ==================='
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! ======================================================================
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      end 
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      function Exyz(natoms,Xyz)
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        use Path_module, only : order
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   IMPLICIT NONE
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     integer, parameter :: KINT = kind(1)
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     integer, parameter :: KREAL = kind(1.0d0)
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      INTEGER(KINT) ,INTENT(IN) :: natoms
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      REAL(KREAL) ,INTENT(IN) :: Xyz(natoms,3)
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      REAL(KREAL) :: Exyz
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      INTEGER(KINT) :: i
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      REAL(KREAL) :: dCH,dNH,dCN
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      real(KREAL) :: autoA,autoeV
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      parameter (autoA=0.52917715d0)
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      parameter (autoeV=27.21183d0)
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      real(KREAL) :: Q(3)
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      real(KREAL) :: TT,gR,pR
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      real(KREAL) :: mB,mC,mH
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      real(KREAL) :: T,RN,RC,r1,r2,r3
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      real(KREAL) :: Z1,Z12,V1
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      real(KREAL) :: Z2,Z22,V2
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      real(KREAL) :: Z3,Z32,V3
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      real(KREAL) :: S1,S2,S3,S12,S22,S32,POLY
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      real(KREAL) :: E1,E2,E3,HY1,HY2,HY3,SWITCH,V123
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      LOGICAL :: Debug
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      LOGICAL, SAVE :: First=.TRUE.
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  INTERFACE
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     function valid(string) result (isValid)
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       CHARACTER(*), intent(in) :: string
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       logical                  :: isValid
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     END function VALID
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  END INTERFACE
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  debug=valid('exyz')
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      dCN=0.
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      dCH=0.
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      dNH=0.
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      do i=1,3
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         dCN=dCN+(xyz(Order(3),i)-xyz(order(2),i))**2
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         dCH=dCH+(xyz(order(1),i)-xyz(order(2),i))**2
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         dNH=dNH+(xyz(order(1),i)-xyz(order(3),i))**2
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      end do
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      R1=sqrt(dCH)
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      R2=sqrt(dCN)
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      R3=sqrt(dNH)
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      IF (debug.AND.First) THEN
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         WRITE(*,*) "Exyz in Test, dCH,dCN,dNH:",R1,R2,R3
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      END IF
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!      R1=R1*autoA
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!      R2=R2*autoA
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!      R3=R3*autoA
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!.....CH
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      Z1=R1-1.0823
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      Z12=Z1*Z1
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      V1=-2.8521*(1.0+5.5297*Z1+8.7166*Z12+5.3082*Z1*Z12)*dexp(-5.5297*Z1)
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!.....CN
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      Z2=R2-1.1718
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      Z22=Z2*Z2 
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      V2=-7.9282*(1.0+5.2448*Z2+7.3416*Z22+4.9785*Z2*Z22)*dexp(-5.2448*Z2)
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!.....NH
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      Z3=R3-1.0370
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      Z32=Z3*Z3
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      V3=-3.9938*(1.0+3.0704*Z3)*dexp(-3.0704*Z3)
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!     write(6,*) v1,v2,v3
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!.....THREE BODY TERMS
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      Z1=R1-1.9607
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      Z2=R2-2.2794
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      Z3=R3-1.8687
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      S1=0.4436*Z1+0.6091*Z2+0.6575*Z3
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      S2=-.8941*Z1+0.2498*Z2+0.3718*Z3
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      S3=0.0622*Z1-0.7527*Z2+0.6554*Z3
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      S12=S1*S1
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      S22=S2*S2
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      S32=S3*S3
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      POLY=-3.0578*(1.0+1.9076*S1-0.5008*S2-0.0149*S3+0.6695*S12  &
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          -1.3535*S22-1.0501*S32+0.2698*S1*S2-1.1120*S1*S3        &
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          +1.9310*S2*S3-0.0877*S1*S12+0.0044*S2*S22+0.0700        &
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          *S3*S32+0.0898*S12*S2-1.0186*S1*S22-0.0911*S12          &
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          *S3+0.0017*S1*S32+0.4567*S22*S3-0.8840*S2*S32           &
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          +0.3333*S1*S2*S3-0.0367*S12*S12+0.4821*S22*S22          &
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          +0.2564*S32*S32-0.0017*S12*S1*S2-0.2278*S12*S22         &
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          -0.1287*S1*S2*S22+0.1759*S1*S12*S3-0.0399*S12*S32       &
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          -0.1447*S1*S3*S32-0.3147*S2*S22*S3+0.1233*S22*S32       &
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          +0.3161*S2*S3*S32+0.0919*S12*S2*S3-0.0954*S1*S22*S3     &
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          +0.1778*S1*S2*S32-0.1892*S22*S22*S2)
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      E1=dexp(3.9742*Z1/2.)
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      E2=dexp(4.3688*Z2/2.)
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      E3=dexp(1.5176*Z3/2.)
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      HY1=(E1-1.0/E1)/(E1+1.0/E1)
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      HY2=(E2-1.0/E2)/(E2+1.0/E2)
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      HY3=(E3-1.0/E3)/(E3+1.0/E3)
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      SWITCH=(1.0-HY1)*(1.0-HY2)*(1.0-HY3)
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      V123=SWITCH*POLY
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!     write(6,*) v123,V1+V2+V3+V123
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      Exyz=(V1+V2+V3+V123)/autoeV
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      First=.FALSE.
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      return
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      end function Exyz
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      function Exyz2(natoms,Xyz)
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   IMPLICIT NONE
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     integer, parameter :: KINT = kind(1)
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     integer, parameter :: KREAL = kind(1.0d0)
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      INTEGER(KINT) ,INTENT(IN) :: natoms
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      REAL(KREAL) ,INTENT(IN) :: Xyz(natoms,3)
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      REAL(KREAL) :: Exyz
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     INTEGER(KINT) :: i,j,iat,jat
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     REAL(KREAL) :: Exyz2
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      real(KREAL) :: autoA,autoeV
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      parameter (autoA=0.52917715d0)
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      parameter (autoeV=27.21183d0)
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      real(KREAL) :: Q(3)
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      real(KREAL) :: TT,gR,pR
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      real(KREAL) :: mB,mC,mH
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      real(KREAL) :: T,RN,RC,r1,r2,r3
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      real(KREAL) :: Z1,Z12,V1
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      real(KREAL) :: Z2,Z22,V2
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      real(KREAL) :: Z3,Z32,V3
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      real(KREAL) :: S1,S2,S3,S12,S22,S32,POLY
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      real(KREAL) :: E1,E2,E3,HY1,HY2,HY3,SWITCH,V123
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      Exyz=0.
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      do jat=1,natoms
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         do iat=1,3
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         Exyz=Exyz+(3*iat-3+jat)*xyz(jat,iat)**2
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         end do
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      end do
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      Exyz2=Exyz
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      return
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      end function Exyz2