Eliminating spin contamination in auxiliary-field quantum Monte Carlo: realistic potential energy curve of F2

Abstract

The use of an approximate reference state wave function |Phi_r> in electronic many-body methods can break the spin symmetry of Born-Oppenheimer spin-independent Hamiltonians. This can result in significant errors, especially when bonds are stretched or broken. A simple spin-projection method is introduced for auxiliary-field quantum Monte Carlo (AFQMC) calculations, which yields spin-contamination-free results, even with a spin-contaminated |Phi_r>. The method is applied to the difficult F2 molecule, which is unbound within unrestricted Hartree-Fock (UHF). With a UHF |Phi_r>, spin contamination causes large systematic errors and long equilibration times in AFQMC in the intermediate, bond-breaking region. The spin-projection method eliminates these problems, and delivers an accurate potential energy curve from equilibrium to the dissociation limit using the UHF |Phi_r>. Realistic potential energy curves are obtained with a cc-pVQZ basis. The calculated spectroscopic constants are in excellent agreement with experiment.

8 pages, 6 figures, submitted to J. Chem. Phys

References in corpus (8)

• A Constrained Path Monte Carlo Method for Fermion Ground States
• Quantum Monte Carlo method using phase-free random walks with Slater determinants
• Auxiliary-field quantum Monte Carlo calculations of molecular systems with a Gaussian basis
• Phaseless auxiliary-field quantum Monte Carlo calculations with planewaves and pseudopotentials--applications to atoms and molecules
• Bond breaking with auxiliary-field quantum Monte Carlo
• Auxiliary-field quantum Monte Carlo study of TiO and MnO molecules
• Auxiliary-field quantum Monte Carlo study of first- and second-row post-d elements
• A study of H+H${}_2$ and several H-bonded molecules by phaseless auxiliary-field quantum Monte Carlo with planewave and Gaussian basis sets

Cited by in corpus (32)

• Ab initio computations of molecular systems by the auxiliary-field quantum Monte Carlo method
• Benchmark study of the two-dimensional Hubbard model with auxiliary-field quantum Monte Carlo method
• Resonating valence bond wave function with molecular orbitals: Application to first-row molecules
• Symmetry in Auxiliary-Field Quantum Monte Carlo Calculations
• Pressure-induced diamond to beta-tin transition in bulk silicon: a near-exact quantum Monte Carlo study
• Variational Benchmarks for Quantum Many-Body Problems
• Excited state calculations using phaseless auxiliary-field quantum Monte Carlo: potential energy curves of low lying C2 singlet states
• Singlet-Triplet Energy Gaps of Organic Biradicals and Polyacenes with Auxiliary-Field Quantum Monte Carlo
• Assessing weak hydrogen binding on Ca+ centers: An accurate many-body study with large basis sets
• An Auxiliary-Field Quantum Monte Carlo Study of the Chromium Dimer
• Phaseless Auxiliary-Field Quantum Monte Carlo on Graphical Processing Units
• Computation of ground-state properties in molecular systems: back-propagation with auxiliary-field quantum Monte Carlo
• Chemical Transformations Approaching Chemical Accuracy via Correlated Sampling in Auxiliary-Field Quantum Monte Carlo
• The Stability, Energetics, and Magnetic States of Cobalt Adatoms on Graphene
• Utilizing Essential Symmetry Breaking in Auxiliary-Field Quantum Monte Carlo: Application to the Spin Gaps of the C${}_{36}$ Fullerene and an Iron Porphyrin Model Complex
• Polishing the Gold Standard: The Role of Orbital Choice in CCSD(T) Vibrational Frequency Prediction
• Frozen-orbital and downfolding calculations with auxiliary-field quantum Monte Carlo
• Calculation of interatomic forces and optimization of molecular geometry with auxiliary-field quantum Monte Carlo
• Ab Initio Many-body Study of Cobalt Adatoms Adsorbed on Graphene
• The performance of phaseless auxiliary-field quantum Monte Carlo on the ground state electronic energy of benzene
• Stochastic Resolution-of-the-Identity Auxiliary-Field Quantum Monte Carlo: Scaling Reduction without Overhead
• Constrained-Path Auxiliary-Field Quantum Monte Carlo for Coupled Electrons and Phonons
• A comparison between the one- and two-step spin-orbit coupling approaches based on the ab initio Density Matrix Renormalization Group
• Unbiasing Fermionic Auxiliary-Field Quantum Monte Carlo with Matrix Product State Trial Wavefunctions
• Open-Shell Coupled-Cluster Valence-Bond Theory Augmented with an Independent Amplitude Approximation for Three-Pair Correlations: Application to a Model Oxygen-Evolving Complex and Single Molecular Magnet
• Reduced Scaling Hilbert Space Variational Monte Carlo
• Qualitative breakdown of the unrestricted Hartree-Fock energy
• Interfacing branching random walks with Metropolis sampling: constraint release in auxiliary-field quantum Monte Carlo
• Ab initio Calculations in Atoms, Molecules, and Solids, Treating Spin-Orbit Coupling and Electron Interaction on Equal Footing
• Adsorption and Diffusion of F2 molecules on Pristine Graphene
• Self-Refinement of Auxiliary-Field Quantum Monte Carlo via Non-Orthogonal Configuration Interaction
• Implementing advanced trial wave functions in fermion quantum Monte Carlo via stochastic sampling