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2D Relaxed Surface Scan with MCSCF and XMCQDPT2

Panwang Zhou

Hi, all

I want to do a 2D relaxed surface scan with MCSCF, and then do a energy calculation on this surface with XMCQDPT2, I have the following questions:

1) Can I first perform an optimization with MCSCF and then do a XMCQDPT2 energy calcultion with one input file?
If not, the work will become complicated as I need to extract all the optimized geometries and MCSCF MOs from output and punch files, respectively. And I also need to prepare a number of XMCQDPT2 input files.

2) If the answer for the first is no, I plan to write a perl script to do this work rather than use the RSURF in firefly, then I have another question about the natural orbitals:

When the MCSCF was done, there are two types of orbitals in the punch file, one is MCSCF NATURAL ORBITALS, and the other is MCSCF OPTIMIZED ORBITALS. From this discussion club I know the following XMCQDPT2 calculation need the MCSCF OPTIMIZED ORBITALS, my question is:
  which type of orbitals should be used in the next MCSCF calculation, where the geometry is close to the previous one.

I ask this question because I saw the following paragraph in the Molpro manual:
"For a CASPT2 calculation, the zeroth-order Hamiltonian can be brought to a block-diagonal
form when (pseudo)canonical orbitals are used.  This leads to fastest convergence.  It is there-fore recommended that in the preceding MULTI calculation the orbitals are saved using the CANONICAL directive (note that the default is NATORB)."

It seems that the CASSCF should use the natural orbitals and the CASPT2 should use the (pseudo)canonical orbitals.

Best Regards,
Panwang Zhou

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