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QMCPACK / qmcpack

Main repository for QMCPACK, an open-source production level many-body ab initio Quantum Monte Carlo code for computing the electronic structure of atoms, molecules, and solids with full performance portable GPU support
http://www.qmcpack.org
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Why is short-range potential LR_rc != Rws, the image radius? #699

Open Paul-St-Young opened 6 years ago

Paul-St-Young commented 6 years ago

Uniform3DGridLayout::SetLRCutoffs duplicates the functionality of LatticeAnalyzer<T,3>::calcSimulationCellRadius and sets the short-range cutoff for the Coulomb potential to the simulation cell radius (Rsc). This is different from the default short-range cutoff radius of Jastrow and back flow functions set in BsplineJastrowBuilder and BackflowBuilder, respectively. The Bspline functor cutoff radius defaults to the image radius a.k.a. radius of the Cartesian space Wigner-Seitz cell (Rws).

For a non-orthorhombic cell, Rws>Rsc. My understanding is that Rws is the optimal cutoff radius for short-range functions. Therefore it bothers me to see the potential cutoff set to Rsc. Since the potential cutoff rc has no effect on the Ewald sum (so long as rc*kc is constant), is there any reason not to set rc=Rws? This would make potential and wavefunction consistent and help avoid confusion between Rsc and Rws.

prckent commented 6 years ago

Agreed. I think you have found an historical inconsistency. Rc=Rws would be more consistent.