B1. I have set all the parameters in the Jastrow factor to zero, but the VMC energy that I get differs from the expected (Hartree-Fock) energy. What’s wrong?

To remove the Jastrow, you need to delete all parameters (except the cutoffs) from all Jastrow terms in the correlation.data file. CASINO will apply the cusp conditions on the Jastrow parameters (=> non-zero alpha_1 parameter) if any parameter is provided in the file, even if it’s zero.

Alternatively, you can set ‘use_jastrow : F‘ in the input file, provided you do not want to optimize the Jastrow parameters in this run.

MDT Note added 9/10/2013: the default behaviour for empty Jastrows in energy minimization changed in CASINO v2.13.94, so that it now does the following:

If one is studying a homogeneous system, or a 3D-periodic system, or the optimization method is energy minimisation with the CASINO standard Jastrow factor, a simple default for u will be chosen that satisfies the Kato cusp conditions; otherwise, only the Slater wave function will be used for the first configuration generation run when performing wave function optimization” (varmin, madmin, or emin).

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