LCAOStart
LCAOStart
Section SCF::LCAO
Type integer
Before starting a SCF calculation, Octopus can perform
a linear combination of atomic orbitals (LCAO) calculation.
These can provide Octopus with a good set
of initial wavefunctions and with a new guess for the density.
(Up to the current version, only a minimal basis set is used.)
The default is lcao_states if at least one species representing an atom is present.
The default is lcao_none if all species are species_user_defined,
species_charge_density, species_from_file, or species_jellium_slab.
The initial guess densities for LCAO are taken from the atomic orbitals for pseudopotential species; from the natural charge density for species_charge_density, species_point, species_jellium, and species_jellium_slab; or uniform for species_full_delta, species_full_gaussian, species_user_defined, or species_from_file. Pseudopotential species use the pseudo-wavefunctions as orbitals, full-potential atomic species (species_full_delta and species_full_gaussian) use hydrogenic wavefunctions, and others use harmonic-oscillator wavefunctions.
Note: Some pseudopotential files (CPI, FHI for example) do not contain full information about the orbitals. In this case, Octopus generates the starting density from the normalized square root of the local potential. If no orbitals are available at all from the pseudopotential files, Octopus will not be able to perform an LCAO and the initial states will be randomized.
Options:
- lcao_none:
Do not perform a LCAO calculation before the SCF cycle. Instead use random wavefunctions.
- lcao_states:
Do a LCAO calculation before the SCF cycle and use the resulting wavefunctions as
initial wavefunctions without changing the guess density.
This will speed up the convergence of the eigensolver during the first SCF iterations.
- lcao_full:
Do a LCAO calculation before the SCF cycle and use the LCAO wavefunctions to build a new
guess density and a new KS potential.
Using the LCAO density as a new guess density may improve the convergence, but can
also slow it down or yield wrong results (especially for spin-polarized calculations).