qcinput 0.5.0

Generate quantum chemistry input files from molecular structures

qcinput

qcinput is a CLI tool that reads an xyz or gjf geometry, loads task type and keywords from TOML, and writes an ORCA or Gaussian input file.

Install With pip

pip install qcinput

For development (from source):

pip install -e .

Usage

qcinput generate <path/to/structure.xyz|.gjf> [-c|--config <path/to/qcinput.toml>] [-o output.inp]

Compatibility shorthand (same behavior):

qcinput <path/to/structure.xyz|.gjf> [-c|--config <path/to/qcinput.toml>] [-o output.inp]

Show version:

qcinput --version
qcinput -V

First-time setup:

qcinput init-config
qcinput init-config --kind int
qcinput init-config --kind ts
qcinput init-config --kind sp

init-config always writes int/ts/sp task sections in one TOML file; --kind only sets the initial active value of [qcinput].kind.

Default config path:

./qcinput.toml

You can override this with:

QCINPUT_CONFIG=/path/to/config.toml qcinput water.xyz

Example:

qcinput water.xyz -c qcinput.toml -o water_opt.inp

For ORCA and Gaussian, kind = "ts" now uses a two-step TS template. Use:

qcinput water.xyz -c qcinput.toml -o water_ts.inp

ORCA TS settings:

[orca.task.ts]
step1_keywords = ["Opt"]
step2_keywords = ["OptTS", "Freq"]
constraint_atoms = [[0, 1], [2, 3]]
calc_hess = true

constraint_atoms accepts either one pair ([0, 1]) or multiple pairs ([[0, 1], [2, 3], ...]). ORCA TS uses global [orca].nprocs and [orca].maxcore for the compound workflow. Step-2 reads <output_stem>_Compound_1.xyz.

Gaussian TS settings (Link1):

[gaussian.task.ts]
step1_route = ["Opt=ModRedundant"]
constraint_atoms = [[0, 1], [2, 3]]
step2_route = ["Opt=(TS,CalcFC,NoEigenTest,NoFreeze)", "Freq", "Geom=AllCheck", "Guess=Read"]

constraint_atoms accepts one pair ([0, 1]) or multiple pairs ([[0, 1], [2, 3], ...]) and will be converted to B i j F lines. Legacy modredundant is still supported for compatibility. %chk is auto-generated as <structure_stem>.chk (e.g. water.xyz -> water.chk). This applies to Gaussian int, sp, and ts.

When qcinput.engine = "gaussian", default output suffix is .gjf.

Config Format (TOML)

We use TOML because it is readable for humans, easy to version control, and strongly structured.

[qcinput]
engine = "orca" # or "gaussian"
kind = "int" # int | ts | sp

[molecule]
charge = 0
multiplicity = 1

[orca]
nprocs = 8
maxcore = 4000
base_keywords = ["r2scan-3c", "D4", "def2-mTZVPP"]
extra_keywords = ["TightSCF", "NormalSCF"] # optional, appended at end
smd = false # optional
smd_solvent = "toluene"

[orca.task.int]
keywords = ["Opt", "Freq"]

[gaussian]
nprocshared = 8
mem = "8GB"
method_basis = "B3LYP/def2TZVP"
extra_keywords = ["SCF=Tight"] # optional, appended at end of route

[gaussian.task.int]
route = ["Opt", "Freq"]

Output Snippet

# Generated by qcinput v<version> (https://github.com/yushengyangchem/qcinput)
! Opt Freq r2scan-3c D4 def2-mTZVPP
%pal
  nprocs 8
end
%maxcore 4000
* xyz 0 1
O 0.000000 0.000000 0.000000
H 0.757000 0.586000 0.000000
H -0.757000 0.586000 0.000000
*