MOLPRO

42 GEOMETRY OPTIMIZATION (OPTG) 333
In the last example the monomer structures are kept fixed, and the interaction energy is optimized.
***,HF dimer MP2/CP optimization without monomer relaxation
basis=avtz
gthresh,energy=1.d-8
! INITIAL VALUES OF GEOMETRY VARIABLES
RFF= 5.3
THETA1 = 7
THETA2 = 111
symmetry,x
orient,noorient
geometry={
f1
f2 f1 rff
h1 f1 1.74764059 f2 theta1
h2 f2 1.74764059 f1 theta2 h1 180.} !using fixed HF distances of isolated HF
label:
text, CP calculation for HF1 MONOMER
dummy,f2,h2;
!second hf is now dummy
{hf;accu,16}
!scf for first monomer
mp2;
!mp2 for first monomer
ehf1=energy
!save mp2 energy in variable
forces;
!compute mp2 gradient for first monomer
scale,-1 !multiply gradient by -1
text, CP calculation for HF2 MONOMER
dummy,f1,h1;
{hf;accu,16}
mp2;
ehf2=energy
forces;
add,-1
text, DIMER CALCULATION
dummy
{hf;accu,16}
mp2;
edimer=energy
forces;
add,1
!first hf is now dummy
!scf for second monomer
!mp2 for second monomer
!save mp2 energy in variable
!compute mp2 gradient for first monomer
!subtract from previous gradient
!reset dummies
!scf for dimer
!mp2 for dimer
!save mp2 energy in variable
!compute mp2 gradient for dimer
!add to previous gradient
optg,gradient=.d-5,startcmd=label:
!find next energy
text,optimized geometry parameters
show,rhf,rff,theta1,theta2
text,computed interaction energies
de=(edimer-ehf1-ehf2)*tocm !CPC corrected interaction energy with fixed monomers
http://www.molpro.net/info/current/examples/hfdimer_cpcopt2.com