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We developed a scalable quantum Monte Carlo method for accurate molecular energy calculations. This phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) approach achieves chemical accuracy for many systems.

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Area of Science:

  • Computational Chemistry
  • Quantum Mechanics
  • Materials Science

Background:

  • Accurate prediction of molecular properties is crucial in chemistry and materials science.
  • Quantum Monte Carlo (QMC) methods offer a powerful approach to solving the electronic Schrödinger equation.
  • The phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) method has shown promise but faces challenges with overcorrelation and scalability.

Purpose of the Study:

  • To develop and validate a scalable Fortran implementation of the phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) method.
  • To investigate modifications to the phaseless approximation to mitigate overcorrelation errors.
  • To assess the accuracy and performance of the improved ph-AFQMC method for various molecular systems.

Main Methods:

  • A scalable Fortran implementation of the phaseless auxiliary-field quantum Monte Carlo (ph-AFQMC) was developed.
  • Modifications to the phaseless approximation were investigated to address overcorrelation.
  • The method was applied to the HEAT set of molecules, benzene, and water clusters.

Main Results:

  • The ph-AFQMC implementation demonstrates excellent performance and scaling with system size.
  • A mean absolute energy deviation of 1.15 kcal/mol was achieved for the HEAT set, approaching chemical accuracy.
  • The modified algorithm achieved accuracy comparable to the original scheme for benzene, using fewer basis functions.
  • Excellent binding energies for water clusters were obtained, with typical deviations below 0.5 kcal/mol compared to CCSD(T).

Conclusions:

  • The scalable ph-AFQMC implementation provides an accurate and efficient method for electronic structure calculations.
  • Modifications to the phaseless approximation improve accuracy and reduce computational cost.
  • While systematic errors persist for certain molecules (e.g., CN, CO2, O2), further improvements with more accurate trial wavefunctions are possible.