Transcorrelated methods for multireference problems.

Area of Science:

• Quantum Chemistry
• Computational Physics
• Electronic Structure Theory

Background:

• Accurate electronic structure calculations are crucial for understanding molecular properties.
• Multireference systems pose significant challenges for traditional quantum chemistry methods.
• The transcorrelated method offers a promising route to high accuracy but requires careful treatment of the reference wavefunction.

Purpose of the Study:

• To adapt and apply the transcorrelated method to problems with multireference character.
• To propose and validate a workflow for optimizing the Jastrow factor using multi-configurational reference wavefunctions.
• To achieve highly accurate energies and excitation energies for various molecules.

Main Methods:

• Jastrow factor optimization using multi-configurational reference wavefunctions.
• Transcorrelated-Full Configuration Interaction Quantum Monte Carlo (TC-FCIQMC) within the xTC approximation.
• Application to N2 binding curve, and excitation energies of N2, CO, and NH3.

Main Results:

• Demonstrated chemical accuracy for the N2 binding curve using the aug-cc-pVTZ basis set.
• Obtained accurate excitation energies for N2, CO, and NH3, comparable to state-of-the-art theoretical methods.
• Showcased the effectiveness of the proposed workflow for Jastrow optimization in multireference systems.

Conclusions:

• The proposed workflow significantly improves the accuracy of the transcorrelated method for multireference problems.
• The method provides highly accurate results with modest basis sets, demonstrating its efficiency.
• This work advances the application of quantum Monte Carlo methods in computational chemistry.