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Evaluating Multiconfigurational Trials for Accurate Phaseless Auxiliary-Field Quantum Monte Carlo on 3d Transition
Hung T Vuong1, Ankit Mahajan1, John L Weber2
1Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, United States.
Journal of Chemical Theory and Computation
|March 3, 2026
Summary
We evaluated trial wave function protocols for phaseless auxiliary field quantum Monte Carlo (ph-AFQMC) in transition metal systems. A configuration interaction singles and doubles (CISD) trial state in ph-AFQMC achieved the highest accuracy for ionization potentials.
Area of Science:
- Quantum chemistry
- Computational physics
- Materials science
Background:
- Accurate prediction of electronic properties for transition metal systems is crucial.
- Phaseless auxiliary field quantum Monte Carlo (ph-AFQMC) offers a promising approach for high-accuracy calculations.
- Evaluating different trial wave function protocols is essential for optimizing ph-AFQMC performance.
Purpose of the Study:
- To assess multiconfigurational trial wave function protocols for ph-AFQMC on transition metal systems.
- To benchmark vertical ionization potentials (VIPs) against experimental and high-accuracy computational data.
- To identify the most accurate and cost-effective ph-AFQMC protocol for these systems.
Main Methods:
- Benchmarking ph-AFQMC with various trial wave functions (including CISD) for VIPs of transition metal complexes.
- Comparison with coupled-cluster theory methods (CCSD(T) and DLPNO-CCSD(T1)).
- Extrapolation to the complete-basis-set (CBS) limit using different schemes.
Main Results:
- ph-AFQMC with a CISD trial state demonstrated the closest agreement with experimental ionization potentials (<2 kcal/mol errors).
- A combination of ph-AFQMC with a triple-ζ basis and DLPNO-CCSD(T1) CBS correction provided good accuracy at a modest computational cost.
- The performance of different trial states and basis sets was systematically analyzed.
Conclusions:
- The CISD trial state in ph-AFQMC is highly accurate for ionization potentials in transition metal systems, despite scalability limitations.
- Optimized ph-AFQMC protocols, combined with CBS extrapolation, can achieve near-experimental accuracy for challenging systems.
- This work provides valuable insights for selecting appropriate computational methods for transition metal chemistry.
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