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Quantum Monte Carlo

The Algorithm for performing a variational Monte Carlo calculations runs thus as this

  • Initialisation: Fix the number of Monte Carlo steps. Choose an initial \boldsymbol{R} and variational parameters \alpha and calculate \left|\psi_T^{\alpha}(\boldsymbol{R})\right|^2 .
  • Initialise the energy and the variance and start the Monte Carlo calculation.
    • Calculate a trial position \boldsymbol{R}_p=\boldsymbol{R}+r*step where r is a random variable r \in [0,1] .
    • Metropolis algorithm to accept or reject this move w = P(\boldsymbol{R}_p)/P(\boldsymbol{R}) .
    • If the step is accepted, then we set \boldsymbol{R}=\boldsymbol{R}_p .
    • Update averages
  • Finish and compute final averages.
Observe that the jumping in space is governed by the variable step. This is Called brute-force sampling. Need importance sampling to get more relevant sampling, see lectures below.