Transcorrelated selected configuration interaction in a bi-orthonormal basis and with a cheap three-body correlation...

Area of Science:

• Quantum chemistry
• Computational chemistry
• Theoretical chemistry

Background:

• Standard selected configuration interaction (SCI) methods often face challenges with accuracy in correlated calculations.
• Transcorrelated (TC) methods offer a route to incorporate electron correlation but require careful basis set selection.
• Hartree-Fock (HF) orbitals can lead to significant errors in TC calculations, particularly for properties like ionization potentials and atomization energies.

Purpose of the Study:

• To develop a mathematical framework for SCI within a bi-orthogonal basis for TC calculations.
• To investigate the advantages of a bi-orthogonal basis over standard HF orbitals in TC methods.
• To assess the accuracy and applicability of the proposed BiO-TC-SCI approach for molecular property calculations.

Main Methods:

• Development of a mathematical framework for SCI using a bi-orthogonal basis in TC calculations.
• Comparison of results obtained with bi-orthogonal orbitals versus HF orbitals.
• Implementation of a simple, user-friendly three-body correlation factor.
• Testing the approach on atomization energies for 14 molecules and bond dissociation processes.

Main Results:

• The bi-orthogonal basis enables a proper definition of the frozen core approximation in TC-SCI.
• Bi-orthogonal orbitals significantly reduce errors in ionization potentials and atomization energies compared to HF orbitals.
• The optimized bi-orthogonal basis reduces the positive part of the second-order energy (PT2), aiding extrapolation techniques.
• Accurate atomization energies were obtained for 14 molecules, and size-consistent double bond breaking was achieved.

Conclusions:

• The BiO-TC-SCI approach provides a robust and accurate method for electronic structure calculations.
• The use of a bi-orthogonal basis overcomes limitations associated with HF orbitals in TC methods.
• The simplified correlation factor makes the BiO-TC-SCI method practical for complex molecular systems.