qccodec

qccodec knows how to talk to quantum chemistry programs. For each program it has one codec that turns a qcdata ProgramInput into the program's native input files and command, and turns the program's output back into structured qcdata results.

qccodec never runs anything itself. qccompute runs the program and uses the codec on both ends, so most scientists use the two together.

Install

python -m pip install qccompute   # also installs qccodec

You also need the program itself; each program page says how to install it and get it found.

Run a calculation

from qcdata import CalcType, Model, ProgramInput, Structure
from qccompute import compute

prog_input = ProgramInput(
    program="psi4",
    calctype=CalcType.gradient,
    structure=Structure(
        symbols=["O", "H", "H"],
        geometry=[[0.0, 0.0, 0.0], [0.524, 1.687, 0.48], [1.146, -0.45, -1.354]],
    ),
    model=Model(method="wb97x-d", basis="def2-svp"),
    keywords={"d_convergence": 1e-8},  # Psi4's own option names
)
output = compute(prog_input)
print(output.results.energy, output.results.gradient)

Every program page has complete, runnable scripts like this one for each calculation type it supports, with every common option shown and the program's quirks explained. Copy one, delete what you don't need, and run it.

Supported programs

program	Calculation types	Notes
crest	energy, gradient, hessian, optimization, conformer_search	GFN-xTB and GFN-FF built in
geometric	optimization, transition_state	Drives any gradient program
orca	energy, gradient, hessian, optimization, transition_state
psi4	energy, gradient, hessian, optimization, transition_state	Any Psi4 method; point charges for QM/MM
terachem	energy, gradient, hessian, optimization	GPU quantum chemistry
terachem-fe, terachem-pbs	energy, gradient	TeraChem servers through tcpb
xtb	energy, gradient, hessian, optimization	GFN0/1/2-xTB, GFN-FF, g-xTB

Without qccompute

qccodec also works on its own: decode output you already have into qcdata objects, or write a codec for a program that isn't supported yet.

The QC Suite

• qcref: physical constants, conversion factors, the periodic table, and solvent properties, each with its source.
• qcdata: data structures for quantum chemistry inputs and results.
• qcinf: cheminformatics algorithms for qcdata structures.
• qccodec: program-specific encoders and parsers (this site).
• qccompute: runs programs and returns structured results.
• BigChem and ChemCloud: distributed and cloud execution of qccompute calculations.