state_histogram options

The state_histogram table contains options used to control the options for calculating the state histograms during a Full Configuration Interaction Quantum Monte Carlo or Density Matrix Quantum Monte Carlo simulation.

This is a generalization of the state histograms original proposed by Cleland and coworkers for FCIQMC: [Cleland12]. The generalization is to treat DMQMC in addition to FCIQMC. In the case of FCIQMC the behavior is nearly identical to that of the original algorithm.

In FCIQMC, the histograms are calculate based on the excitation levels relative to the reference determinant. In DMQMC, we add an additional excitation index based on the excitation level between the two determinants used to label the density matrix site.

report_frequency

type: integer.

Optional. Default: nreports

The frequency in report cycles to calculate and report the state histograms. A histogram is always reported at the beginning and end of a calculation regardless of whether it falls within the frequency provided.

nbins

type: integer.

Optional. Default: 5

The number of histogram bins to use per decade of walker population. As an example, if we have a walker population 10 to 100, there are bins from: \(\left[10, \sim 15.85\right)\), \(\left[15.85, \sim 25.12\right)\), \(\left[25.12, \sim 39.81\right)\), \(\left[39.81, \sim 63.10\right)\), and \(\left[63.10, \sim 100\right)\).

decades

type: integer.

Optional. Default: 3

The number of decades of particle populations to include in the histogram bins past the decades of \(\lfloor \log_{10}(N_w) \rfloor\). Where \(N_w\) is the simulations target_population set in the qmc options.

Note

If this value is too small, and the simulations population grows well pass the target population, the histogram population bins may not cover the number of particle on a single site. In this case the simulation will terminate with an error message to prevent an out of bounds index.

skip_memory_check

type: boolean.

Optional. Default: false.

Controls the memory check performed when collecting state histograms. Normally an estimate is made for the memory cost to store all the state histogram files, if the estimate exceeds 1 gigabyte the calculation will halt. Setting this flag to true will ignore the memory check.