Gradient and Hessian using CCSD and EOM-CCSD

Questions
#1

How to get gradient and hessian for Ground state and Exited state [0,0,0,0,0,1,0,0] of O2 using CCSD and EOM-CCSD?

#2

JOBTYPE = FORCE will give you the gradient. If you do EOM-CCSD, you will need to add cc_state_to_opt to specify for which EOM state you need the gradient. For oxygen, you may want to use EOM-SF-CCSD.

Analytic second derivatives are not yet implemented, so when you specify JOBTYPE = FREQ, the code will compute numeric Hessian by finite differences of first derivatives. In this calculation, you will need to turn off the symmetry.

There are examples of these calculations in the manual and in $QC/samples.

#3

Dear Ma’am,

So I need to do a OPT followed by a FORCE and FREQ calculation. Am I correct?

#4

It depends on what you want. If you just need gradient or Hessian at the particular structure, you can do it the way I described. If you want to have optimized structure and then frequencies, you first do JOBTYPE=OPT, read geometry, and do JOBTYPE=FREQ.