Bundled basis sets

qc-rs ships 229 named basis sets as editable Python data files under python/qc/basis/. The basis chapter is the tutorial; this page is the reference for listing, loading, and customizing the bundled data.

Listing what is available

The names live in qc.basis.baslib_filename (a dict of name → module_stem):

from qc import basis
len(basis.baslib_filename)                 # 229
"cc-pvtz" in basis.baslib_filename         # True
sorted(n for n in basis.baslib_filename if n.startswith("def2"))

Any of these names is a valid ao= (or rijk=/ric=) value in qc.chk.new(...). The main families:

family	examples	notes
Pople	3-21g, 6-31g, 6-31g*, 6-31+g**, 6-311g**, 6-311++g**	split-valence
Dunning cc	cc-pvdz, cc-pvtz, cc-pvqz, aug-cc-pvdz, cc-pvdz-pp	correlation-consistent; -pp carries an ECP
Karlsruhe def2	def2-svp, def2-tzvp, def2-qzvp, def2-tzvpd	built-in ECP for heavy elements (Rb onward)
auxiliary	cc-pvdz-jkfit, cc-pvdz-ri/mp2fit, def2-universal/jkfit	RI fitting sets (rijk=/ric=)

The data files

Each file (except the _00* utilities) is a basis-set data file: it defines one module-level variable per element (named after the symbol — H, He, Li, …) as an nwchem_format(...) object:

import importlib
cc_pvdz = importlib.import_module("qc.basis.cc_pvdz")
h = cc_pvdz.H
h.description     # "cc-pvdz:H"
h.inpdata         # the NWChem-format orbital-shell text
h.ecp             # None (or the ECP text, for *-pp / def2 heavy elements)

The nwchem_format object

class nwchem_format:
    inpdata      # str: NWChem orbital-basis text (one element)
    description  # str or None: a human-readable label
    ecp          # str or None: NWChem ECP text (None for all-electron)

inpdata is parsed by the Rust qc_mol::nwchem::parse() when qc.chk.new(ao=...) is called.

NWChem text format

SYMBOL  SHELL_TYPE
  exponent  coeff1  coeff2  ...
  exponent  coeff1  coeff2  ...

• SHELL_TYPE: S, P, D, F, G, H, I, K, or SP (auto-split into S and P).

• Multiple coefficient columns → a generally-contracted shell.

H    S
     13.0100000   0.0196850
      1.9620000   0.1379770
      0.4446000   0.4781480
H    S
      0.1220000   1.0000000
H    P
      0.7270000   1.0000000

Do not apply primitive normalization by hand — qc-mol does it once from the raw coefficients.

Using a custom basis

Inline, per element

Build an nwchem_format object and hand it to ao= (as a dict value):

from qc.basis import nwchem_format
import qc

myN = nwchem_format("""
N S
  242.766  0.0598657
   36.485  0.352955
    7.814  0.706513
N P
    5.425  0.237972
    1.149  0.858953
""", description="custom:N")

m = qc.chk.new(atom="N 0 0 0; N 0 0 1.1", ao={"N": myN}, unit="angstrom")

Editing or adding a bundled set

The files are plain Python, so you can edit an element’s block in place, or add a new <name>.py data file and register it in baslib_filename. After editing, rebuild the extension (make install / maturin develop) so the change is picked up. Full editing/adding workflow: docs/qc-basis.md.

ECP-bearing bases

The correlation-consistent -pp sets and the def2 sets carry their effective-core potential inline (in the ecp field). qc.chk.new(ao="def2-svp") on a heavy atom therefore runs valence-only automatically — no separate ecp= argument — matching PySCF’s basis="def2-svp", ecp="def2-svp". The def2 JK-fit auxiliary is the universal def2-universal/jkfit.