List of Forte2 capabilities

Forte2 is still under active development, with a focus on multi-reference and relativistic methods. Here is a (non-exhaustive) list of the current capabilities of Forte2:

• Support for density-fitted or Cholesky-decomposed integrals (no support for conventional, 4-index integrals)

• Support for arbitrary model Hamiltonians

• Support for utilizing molecular symmetry (largest Abelian subgroup) at the post-Hartree-Fock level

• Support for the finite (Gaussian-distributed) nuclear charge model [1]

• Scalar and vector relativistic Hamiltonians

  • Spin-free 1-electron exact two-component (sf-1eX2C) [2]

  • Spin-orbit 1-electron exact two-component (so-1eX2C) [2]

  • Various empirical scaling schemes to approximate two-electron spin-orbit couplings (“Boettger factors”) [3]

• Flavors of Hartree-Fock theory

  • Restricted Hartree-Fock (RHF)

  • Restricted Open-Shell Hartree-Fock (ROHF)

  • Unrestricted Hartree-Fock (UHF)

  • Constrained unrestricted Hartree-Fock (CUHF)

  • Generalized Hartree-Fock (GHF)

• A flexible configuration interaction (CI) module

  • Spin-adapted CI (CSF basis) for non-relativistic Hamiltonians

  • Support for generalized active spaces (GAS) / occupation-restricted multiple active spaces (ORMAS)

  • Two-component CI for relativistic Hamiltonians

  • Heat-bath configuration interaction (HBCI) with support for excited states and occupation restrictions [7]

• Multi-configuration self-consistent field (MCSCF) methods

  • Support for CAS-SCF and GAS-SCF/ORMAS-SCF, with state-averaging

  • Two-component CAS/GAS/ORMAS-SCF

  • Atomic valence active space (AVAS) active space selection (support for both one- and two-component Hartree-Fock) [4]

• Multi-reference driven similarity renormalization group (MR-DSRG) methods

  • Non-relativistic DSRG-MRPT2 with reference relaxation and state-averaging [7]

  • Two-component relativistic DSRG-MRPT2 with reference relaxation and state-averaging [8]

• Various orbital manipulation routines

  • Zeroth order active space embedding theory (ASET(0)) [5]

  • Intrinsic atomic orbitals (IAO) [6]

  • Intrinsic bond orbitals (IBO) [6]

  • A cube file generator for visualizing molecular orbitals

References

[1]

Visscher, L.; Dyall, K. G. Dirac-Fock Atomic Electronic Structure Calculations Using Different Nuclear Charge Distributions. Atomic Data and Nuclear Data Tables 1997, 67 (2), 207-224. https://doi.org/10.1006/adnd.1997.0751.

[2] (1,2)

Liu, W.; Peng, D. Exact Two-Component Hamiltonians Revisited. The Journal of Chemical Physics 2009, 131 (3), 031104. https://doi.org/10.1063/1.3159445.

[3]

Ehrman, J.; Martinez-Baez, E.; Jenkins, A. J.; Li, X. Improving One-Electron Exact-Two-Component Relativistic Methods with the Dirac-Coulomb-Breit-Parameterized Effective Spin-Orbit Coupling. J. Chem. Theory Comput. 2023, 19 (17), 5785-5790. https://doi.org/10.1021/acs.jctc.3c00479.

[4]

Sayfutyarova, E. R.; Sun, Q.; Chan, G. K.-L.; Knizia, G. Automated Construction of Molecular Active Spaces from Atomic Valence Orbitals. J. Chem. Theory Comput. 2017, 13 (9), 4063-4078. https://doi.org/10.1021/acs.jctc.7b00128.

[5]

He, N.; Evangelista, F. A. A Zeroth-Order Active-Space Frozen-Orbital Embedding Scheme for Multireference Calculations. The Journal of Chemical Physics 2020, 152 (9), 094107. https://doi.org/10.1063/1.5142481.

[6] (1,2)

Knizia, G. Intrinsic Atomic Orbitals: An Unbiased Bridge between Quantum Theory and Chemical Concepts. J. Chem. Theory Comput. 2013, 9 (11), 4834-4843. https://doi.org/10.1021/ct400687b.

[7] (1,2)

Holmes, A. A.; Umrigar, C. J.; Sharma, S. Excited States Using Semistochastic Heat-Bath Configuration Interaction. J. Chem. Phys. 2017, 147 (16), 164111. https://doi.org/10.1063/1.4998614.

[8]

Li, C.; Evangelista, F. A. Multireference Driven Similarity Renormalization Group: A Second-Order Perturbative Analysis. J. Chem. Theory Comput. 2015, 11 (5), 2097-2108. https://doi.org/10.1021/acs.jctc.5b00134.