MOLPRO

42 GEOMETRY OPTIMIZATION (OPTG) 326
***, HCN NHC Isomerization - Transition State Optimization and Frequencies
l1=1.18268242 ang
l2=1.40745082 ang
a1=55.05153416 degree
basis=3-21G
symmetry,nosym
geometry={
C
N,1,l1
H,2,l2,1,a1}
hf
frequencies,analytical
mp2
! HF-SCF
! Vibrational frequencies for HF-SCF (analytical Hessian)
! MP2
optg,root=2,method=rf,readhess
! Transition State Search using Rational Function Optimizer
frequencies
---
! Vibrational frequencies for MP2 (numerical Hessian)
http://www.molpro.net/info/current/examples/hcn_mp2_ts.com
The second example shows how to do a CCSD(T) optimization with an MP2 hessian. Note
that currently the CCSD(T) gradient is computed numerically using finite energy differences,
and this can take long time for larger molecules. The calculation of the MP2 hessian finite
differences of analytical gradients.
***, HCN NHC Transition State Optimization and Frequencies
rcn=1.18 ang
rnh=1.40 ang
alpha=55 degree
basis=vtz
geometry={
C
N,1,rcn
H,2,rnh,1,alpha}
hf
ccsd(t)
optg,root=2,hessproc=runmp2
frequencies
!Transition state optimization for ccsd(t) using mp2 hessian
!CCSD(T) frequencies (using numerical second derivatives)
runmp2={hf;mp2}
---
!procedure definition
http://www.molpro.net/info/current/examples/hcn_ccsd_ts.com
The last example shows how to do a MRCI+Q (MRCI with Davidson correction) optimization
with an CASPT2 hessian. As for CCSD(T), the MRCI+Q gradient as computed numerically,
while the CASPT2 hessian is obtained using finite differences of analytical CASPT2 gradients.