Psi4 interface

Psi4 is a full-featured open-source quantum chemistry program written in both Python and C++. ASH has an interface both to the Psithon inputfile-based interface of Psi4 but also to the Psi4 Python library.

Psi4Theory class:

class Psi4Theory:
    def __init__(self, psi4dir=None, runmode='library', printsetting='False', psi4settings=None,
                psi4method=None, pe=False, potfile='', filename='psi4_', label='psi4input',
                psi4memory=3000, numcores=1, printlevel=2, fchkwrite=False):

Keyword	Type	Default value	Details
psi4dir	string	None	Path to Psi4 directory. Used by runmode='psithon'
runmode	string	'library'	Psi4 runmode. Options: runmode='library' or runmode='psithon'
printsetting	Boolean	False	Printsetting. If True: Psi4 output is printed to stdout. If False, printing to disk.
psi4settings	dict	None	Psi4 settings dictionary
psi4method	string	None	Psi4 method
pe	Boolean	False	Whether to use polarizable embedding in Psi4 via CPPE library.
potfile	string	''	Name of potential file for in Psi4 CPPE polarizable embedding
filename	string	'psi4'	Name of Psi4 inputfile for psithon runmode.
label	string	None	Optional label of object
psi4memory	integer	3000	Memory in MB used by Psi4
numcores	integer	1	Number of CPU cores Psi4 will use
printlevel	integer	2	The printlevel.
fchkwrite	Boolean	False	XXXX

The Psi4 interface comes in two versions, a library-based interface and an inputfile-based interface. The library interface means that ASH will load Psi4 Python libraries that have to be part of the same Python installation. In the inputfile-based interface (Psithon), ASH will create a Psi4 inputfile in Psithon syntax and will then call a separate Psi4 executable (can be a separate Python installation) via the psi4dir variable (or will find psi4 in shell PATH).

Both interfaces are quite flexible. Most Psi4 settings are controlled by setting the psi4settings dictionary. The Psi4 method is controlled by the psi4method argument. It can be set to a functional name : e.g. 'B3LYP', 'B3LYP-D3BJ' or even 'CCSD' and 'CCSD(T)'. Analytical gradients are available in Psi4 for both CCSD and CCSD(T).

Todo: - Allow to pass dictionaries for other modules

Polarizable Embedding via Psi4 and the CPPE library is possible (described later). Set pe=True and give path to potfile to use.

#Create fragment object from XYZ-file
HF_frag=Fragment(xyzfile='hf.xyz', charge=0, mult=1)
#Psi4 variables defined as a dictionary:
psi4settings={'scf_type': 'pk', 'soscf': True, 'basis' : 'def2-SVP' }
psi4method='b3lyp'

#Psi4: Input-file based interface: using psi4dir to set path
psi4dir='/path/to/psi4_install/bin/psi4'
Psi4calc = Psi4Theory(psi4settings=psi4settings, psi4method=psi4method, runmode='psithon',
                            psi4dir=psi4dir, pe=False, label='psi4input',
                             psi4memory=3000, prinsetting=False)
#Psi4: Library-based interface
Psi4calc = Psi4Theory(psi4settings=psi4settings, psi4method=psi4method, runmode='library',
                            pe=False, label='psi4input', psi4memory=3000)

#Run a single-point energy job
Singlepoint(theory=Psi4calc, fragment=HF_frag)
#An Energy+Gradient calculation
Singlepoint(theory=Psi4calc, fragment=HF_frag, Grad=True)

Parallelization

The Psi4 parallelization is thread-based. The numcores keyword provided to the Psi4-interface is used to specify the number of threads available to Psi4 when the job is run (command-line argument for Psithon and environment variable for library).