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Jastrow Tuning

Before starting a full wavefunction optimization, it is often necessary to "tune" the initial Jastrow factor.

Workflow

  1. Define Jastrow Form: Choose the expansion orders (norda, nordb, nordc).
  2. Initial Parameters: Set initial parameters.
  3. Short VMC: Run a short VMC calculation to check the energy and variance.

Jastrow File Format

The Jastrow file (jastrow.jas) must follow a specific structure.

Example: 3-Body Jastrow

To include a 3-body (e-e-n) Jastrow term (nordc > 0):

jastrow_parameter   1
  5  5  5           norda,nordb,nordc
   0.60000000         scalek
   0.0 0.0 -0.4 -0.2 -0.04 0.08  (a parameters for atom type 1)
   0.0 0.0 -0.1 -0.01 0.01 0.01  (a parameters for atom type 2)
   0.5 0.37 0.07 0.01 -0.01 -0.01 (b parameters)
   (c parameters for atom type 1)
   (c parameters for atom type 2)
end

Key Parameters: - norda: Order of electron-nucleus terms (one set per atom type). - nordb: Order of electron-electron terms (one set for all). - nordc: Order of electron-electron-nucleus terms (one set per atom type).

See Jastrow Factors for the full specification of the file format and parameter counts.

Tuning Strategy

  1. Start Simple: Use nordc=0 (no 3-body) initially.
  2. Optimize Jastrow: Use ioptjas=1 in VMC to optimize the parameters.
  3. Add 3-Body: Once 1- and 2-body terms are good, increase nordc and re-optimize.