Interface to the CFOUR program package (www.cfour.de, free for academic use). CFOUR (Coupled-Cluster techniques for Computational Chemistry) package implements high-level QM calculations. An important feature is the availability of analytic first and second energy derivatives for the coupled clusters methods.

The interface was developed and tested with version 1 of CFOUR. For CCSD and CCSD(T) calculations, externally provided MRCC program can be used.

- hf - supports calculation of energy, gradient, hessian
- mp2 - supports calculation of energy, gradient, hessian
- mp4 - supports calculation of energy
- ccsd - supports calculation of energy, gradient, hessian
- ccsd(t) - supports calculation of energy, gradient, hessian

- cfour_bin_dir
- cfour_bin_dir_mpi
- cfour_force_mrcc
- cfour_genbas_file
- cfour_keywords
- cfour_ld_path
- cfour_mrcc_bin_dir

- basisset
- basisset_zeta
- charge
- correlation_convergence
- correlation_frozen_core
- delete_large_files
- density_convergence
- existing_calc_dir
- job_cleanup
- mem
- method
- multiplicity
- parallel
- parallel_mode
- scf_cycles
- use_symmetry

The following examples, along with all other files needed to run them, can be found in the directory cuby4/interfaces/cfour/examples

```
#===============================================================================
# CFOUR example 1: optimization and vibrational analysis at CCSD(T) level
#===============================================================================
# Optimization and vibrational frequencies calculation of water molecule
# at CCSD(T) level (small basis set is used to make the example run fast)
# CFOUR is one of very few codes that calculate the energy derivatives
# at CCSD(T) level analytically.
# The Multistep protocl is used to run the optimization and frequency
# calculations in one input file
job: multistep
steps: optimization, frequencies
# Optimization step
calculation_optimization:
job: optimize
opt_quality: 0.1
geometry: |
O -0.702196054 -0.056060256 0.009942262
H -1.022193224 0.846775782 -0.011488714
H 0.257521062 0.042121496 0.005218999
# Frequencies calculation
calculation_frequencies:
job: frequencies
geometry: optimized.xyz # Read the optimized geometry from the previous step
#-------------------------------------------------------------------------------
# Common setup
#-------------------------------------------------------------------------------
# The method is the same in both steps, CFOUR interface is used
calculation_common:
# The following setup is shared by all the steps
interface: cfour
method: ccsd(t)
basisset: 6-31G
charge: 0
#-------------------------------------------------------------------------------
# Interface configuration
#-------------------------------------------------------------------------------
# Minimal setup needed for serial calculations
# Path to CFOUR binaries
cfour_bin_dir: /home/rezac/bin/cfour/cfour_v1_64bit/bin
# Path to the GENBAS file containg basis sets
cfour_genbas_file: /home/rezac/bin/GENBAS
```