Methods are encoded in the following format: PMETHODparameters, where

• P – optional capital letter denoting SCF type: 'R' for restricted and 'U' for unrestricted (spin polarized) SCF
• METHOD – capitalized name of the method itself (also allowed are digits,+,-)
• parameters – parameters (basis set, force field etc), must start with a small letter

Method

Name of the method itself includes core method optionally followed by a suffix separated by '-'. Examples of methods

• Empirical potentials
  • EEP – generic Element-wise Empirical Potential (LAMMPS-compatible prm-file is required)
  • OPLS – generic OPLS force field
  • EIM,EAM,COMB,COMB3 – supported in LAMMPS
  • MM3 – supported in TINKER
• Semiempirical methods
  • PM7,PM6,PM6-DH+,PM6-DH2,AM1,PM3,MNDO – supported in MOPAC
  • PDDG,ZINDO – supported in Gaussian
• Ab initio methods
  • HF – Hartree-Fock
  • LDA,LDA-U,GGA,GGA-U,PBE,B3LYP,CAM-B3LYP,HSE06,LC-WPBE,WB97X,WB97XD,M062X,B2PLYP,APF,APFD,PW6B95,PW6B95D3,VDW-DF2,PBE-MBD – DFT methods
  • MP2,MP3,MP4,MP4-SDQ – MP perturbation theory
  • CIS,CID,CISD,QCISD,CI2,CI3,CI4 – CI methods
  • CCD,CCSD,CCSD-T – CC methods

• D3 – Grimme's GD3BJ dispersion correction

Parameters: basis set

Basis set encode four parts: family (in lowercase), size (positive integer), variations (suffix), and k-grid (if calculations are not converged with respect to k-sampling).

In case of multiple sets, they are separated by "x", e.g. "p2pxa3p" means "p2p" for elements up to Ar and "a3p" for heavier elements.

Basis set family:

• a – Ahlrichs, modern version: a2=Def2SV, a2p=Def2SVP, a2pp=Def2SVPP, a3=Def2TZV etc.
• c – Dunning, correlation consistent: c2=cc-pVDZ, c2a=aug-cc-pVDZ, c3=cc-pVTZ etc.
• dg – DGauss: dg2=DGDZVP, dg2p=DGDZVP2, dg3=DGTZVP
• h – Huzinaga as implemented in Firefly or STO-3G in Gaussian
• l – LANL: l2=LANL2DZ, l2p=LANL2DZ ExtraBasis
• p – Pople: p2=6-31G, p2p=6-31G*=6-31G(d), p2pp=6-31G**=6-31G(d,p), p2pa=6-31+G*, p2p3df2pa=6-31+G(3df,2p), p3=6-311G etc.
• s – Stevens (SBK, SBKJC, LFK): s2=CEP-31G, s3=CEP-121G, s2p=CEP-31G*, s2pp=CEP-31G ExtraBasis etc.
• nc – norm conserving pseudopotential
• us – ultrasoft pseudopotential
• paw – projector augmented wave pseudopotential

Basis set size can denote one of

• plane wave energy cutoff in eV
• number of valence orbitals, e.g. 2 for double zeta, 3 for triple zeta etc.
• just the order number within the family

Possible values of the suffix for pseudopotentials are interpreted as in VASP manual ("s" for softer, "h" for harder, "sv", "pv", "d").

Possible values of the suffix for gaussian basis sets are interpreted as follows. A letter may indicate additional functions: "p" polarization orbitals, "a" diffuse orbitals. Immediately after that letter the description may follow. The description of polarization orbitals follows the Gaussian notations with commas and parentheses omitted, e.g. "3df2pd" means 3d plus 1f orbitals for nonhydrogens and 2 sp-orbitals plus 1 d-orbital on hydrogens. The absence of the description implies a default polarization basis ("p" for smaller one, "pp" for larger one), e.g. "p2p"="p2pd", "p2pp"="p2pdp". The description of diffuse orbitals is currently limited to two cases: absence of the description means a diffusion orbital on nonhydrogens, an additional "a" means a diffusion orbital on all atoms. See also Gaussian manual.

Possible values of k-grid currently include Gamma-centered grids in the format "Gn1n2n3", where 1<ni<10 denotes number of k-points in i-th directions. Repetitive "ni" or "ni" fixed by symmetry should not be included, e.g. "G5" for isotropic 2D systems means "G551".