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A PSI4 plugin which performs active-space coupled-cluster (CC) calculations with up to triple excitations, known as CCSDt, and energy corrections based on the method-of-moments of CC, denominated as the CC(t;3) method.
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README.rst

CC(t;3) PSI4 plugin

https://travis-ci.org/piecuch-group/psi4_cct3.svg?branch=dev

CC(t;3) is a quantum chemistry method that consists in the computation of the iterative active-space coupled-cluster approach with singles, doubles, and active-space triples, denominated CCSDt, and in the subsequent energy correction based on the method of moments of coupled-cluster equations.

Compilation

A working version of PSI4 version 1.1 is required. To compile the plugin:

$ git clone https://gitlab.msu.edu/piecuch-group/psi4_cct3
$ cd psi4_cct3
$ `psi4 --plugin-compile`
$ make

Running

In order to run a CCSDt calculation, the following options have to be set within the scheme

set psi4-cct3 {
   option value
   ...
}
froz
Number of frozen core molecular orbitals.
act_occ
Number of active occupied molecular orbitals counting from the fermi vaccum down.
act_unocc
Number of active unnocupied molecular orbitals counting from the fermi vaccum up.
etol
Energy convergence tolerance given as 10^-ETOL. Default is 10^-7
max_iter
Maximum number of iterations. Default is 1000.
keep_amps
If true, write down the converged cluster amplitudes to the file amplitudes.moe.
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