C Energy function is E=d/(a*(x-y)**2+b*(x+y)**2+c) where x is first
C distance y is second distance the a,b,c,d are parameters derived for
C this problem d parameter was set as a penalty currenlty set to 1.
- if ((iabs(j-i).eq.1).or.(iabs(i-k).eq.1)) then
+ if ((iabs(j-i).le.2).or.(iabs(i-k).le.2)) then
eij1=0.0d0
else
- eij1=dtriss/(atriss*(rij-rik)**2+btriss*(rij+rik)**2+ctriss)
+ eij1=dtriss/(atriss*(rij-rik)**2+btriss*(rij+rik)**6+ctriss)
endif
C second case jth atom is center
- if ((iabs(j-i).eq.1).or.(iabs(j-k).eq.1)) then
+ if ((iabs(j-i).le.2).or.(iabs(j-k).le.2)) then
eij2=0.0d0
else
- eij2=dtriss/(atriss*(rij-rjk)**2+btriss*(rij+rjk)**2+ctriss)
+ eij2=dtriss/(atriss*(rij-rjk)**2+btriss*(rij+rjk)**6+ctriss)
endif
C the third case kth atom is the center
- if ((iabs(i-k).eq.1).or.(iabs(j-k).eq.1)) then
+ if ((iabs(i-k).le.2).or.(iabs(j-k).le.2)) then
eij3=0.0d0
else
- eij3=dtriss/(atriss*(rik-rjk)**2+btriss*(rik+rjk)**2+ctriss)
+ eij3=dtriss/(atriss*(rik-rjk)**2+btriss*(rik+rjk)**6+ctriss)
endif
C eij2=0.0
C eij3=0.0
C write(iout,*)i,j,k,eij
C The energy penalty calculated now time for the gradient part
C derivative over rij
- fac=-eij1**2/dtriss*(2.0*atriss*(rij-rik)+2.0*btriss*(rij+rik))
- &-eij2**2/dtriss*(2.0*atriss*(rij-rjk)+2.0*btriss*(rij+rjk))
+ fac=-eij1**2/dtriss*(2.0*atriss*(rij-rik)+6.0*btriss*(rij+rik)**5)
+ &-eij2**2/dtriss*(2.0*atriss*(rij-rjk)+6.0*btriss*(rij+rjk)**5)
gg(1)=xij*fac/rij
gg(2)=yij*fac/rij
gg(3)=zij*fac/rij
gvdwc(l,j)=gvdwc(l,j)+gg(l)
enddo
C now derivative over rik
- fac=-eij1**2/dtriss*(-2.0*atriss*(rij-rik)+2.0*btriss*(rij+rik))
- &-eij3**2/dtriss*(2.0*atriss*(rik-rjk)+2.0*btriss*(rik+rjk))
+ fac=-eij1**2/dtriss*
+ &(-2.0*atriss*(rij-rik)+6.0*btriss*(rij+rik)**5)
+ &-eij3**2/dtriss*(2.0*atriss*(rik-rjk)+6.0*btriss*(rik+rjk)**5)
gg(1)=xik*fac/rik
gg(2)=yik*fac/rik
gg(3)=zik*fac/rik
gvdwc(l,k)=gvdwc(l,k)+gg(l)
enddo
C now derivative over rjk
- fac=-eij2**2/dtriss*(-2.0*atriss*(rij-rjk)+2.0*btriss*(rij+rjk))-
- &eij3**2/dtriss*(-2.0*atriss*(rik-rjk)+2.0*btriss*(rik+rjk))
+ fac=-eij2**2/dtriss*
+ &(-2.0*atriss*(rij-rjk)+6.0*btriss*(rij+rjk)**5)-
+ &eij3**2/dtriss*(-2.0*atriss*(rik-rjk)+6.0*btriss*(rik+rjk)**5)
gg(1)=xjk*fac/rjk
gg(2)=yjk*fac/rjk
gg(3)=zjk*fac/rjk