Towards Large-Scale AFQMC Calculations: Large Time Step Auxiliary-Field Quantum Monte Carlo
arxiv(2024)
摘要
We report modifications of the ph-AFQMC algorithm that allow the use of large
time steps and reliable time step extrapolation. Our modified algorithm
eliminates size-consistency errors present in the standard algorithm when large
time steps are employed. We investigate various methods to approximate the
exponential of the one-body operator within the AFQMC framework, distinctly
demonstrating the superiority of Krylov methods over the conventional Taylor
expansion. We assess various propagators within AFQMC and demonstrate that the
Split-2 propagator is the optimal method, exhibiting the smallest time-step
errors. For the HEAT set molecules, the time-step extrapolated energies deviate
on average by only 0.19 kcal/mol from the accurate small time-step energies.
For small water clusters, we obtain accurate complete basis-set binding
energies using time-step extrapolation with a mean absolute error of 0.07
kcal/mol compared to CCSD(T). Using large time-step ph-AFQMC for the N_2
dimer, we show that accurate bond lengths can be obtained while reducing CPU
time by an order of magnitude.
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