PSI3

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Contents 1 Adding Content to the Page 2 User Manual 3 Installation Manual 4 How To Guides 4.1 CC3 and EOM-CC3

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User Manual

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Installation Manual

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How To Guides

CC3 and EOM-CC3

The CC3 code in PSI is not documented in the PSI user manual. Its capabilities include CC3 and EOM-CC3 with RHF, UHF, and ROHF orbitals. This is currently the only way to include the effect of triple excitations on an excited state, using coupled cluster theory, in the PSI3 package.

The following is a sample input for a ground state CC3 calculation from the PSI test cases:

 psi: (
   label = "CC3 H2O Test"
   wfn = cc3
   reference = rhf
   multp = 1
   basis = "cc-pVDZ"
 
   units = bohr
   % H2O Re geom from Olsen et al., JCP 104, 8007 (1996)
   geometry = (
     O 0.0  0.00000000 -0.00900000
     H 0.0 -1.51526300 -1.05889800
     H 0.0  1.51526300 -1.05889800
   )
 )

The following is a sample input for an EOM-CC3 calculation modified from the PSI test cases:

 psi: (
   label = "CC3 CH"
   jobtype = sp
   wfn = eom_cc3
   reference = rohf
   multi = 2
   docc = (3 0 0 0)
   socc = (0 0 0 1)
   states_per_irrep = (3 0 0 0)
   freeze_core = true
   maxiter = 100
   basis = "cc-pVTZ"
   puream = true
   zmat = (
     C
     H 1 1.1198
   )
 )

This will find three roots with A1 symmetry using EOM-CCSD, but only the lowest will be treated with EOM-CC3.

Keywords to modify a ground state CC3 calculation should be placed in the ccenergy section of the input.

 ccenergy: (
   maxiter = 100
   convergence = 10
 )

Keywords for EOM-CC3 go in the cceom section. The analogous keyword to vectors_per_root, used for EOM-CCSD, is vectors_cc3 for EOM-CC3. These can be important to modify if you are trying to use some obscenely tight convergence criteria for your wavefunction, as in the following:

 cceom: (
   maxiter = 100
   residual_tol = 8
   eval_tol = 12
   vectors_per_root = 30
   vectors_cc3 = 30
 )

Hohenstein 18:20, 30 November 2008 (EST)