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SCFAlgorithms

This page gives hints on how to select the SCF algorithm with the ABINIT package.

Introduction

Self-Consistent Field calculations allow to determine the solution of the Kohn-Sham equations, ending with converged “self-consistent” wavefunctions, density, and Kohn-Sham potentials.

Different algorithms can be chosen to converge to the solution of this set of equations. The input variables iscf governs the choice of density/potential self-consistency algorithms, while wfoptalg focuses on the determination of the wavefunction through the solution of the Schrodinger equation with fixed Kohn-Sham potential.

In the first class of algorithms, selected by iscf), Pulay mixing is one of the most efficient. Also, an efficient preconditioner will speed up the convergence. Among different choices, a generalized Kerker preconditioner is implemented, see diemac, diemix and dielng.
In order to perform a non-self-consistent calculations of wavefunctions and corresponding eigenvalues in a fixed potential, as for representing a full band structure, the loop over density/potentials self-consistency must be disabled, for which iscf=-2 must be chosen.

Among the algorithms to find the wavefunctions, selected by wfoptalg, the conjugate-gradient and the LOBPCG ones are the favourite. The RMM-DIIS algorithm is faster, but might be unstable. Use it for molecular dynamics run or long geometry optimizations. Use the Chebyshev filtering for massive parallel runs.

Inner electronic eigenvalues can be computed thanks to the minimisation of the residual with respect to a target energy value, see eshift.

basic:

  • iscf Integer for Self-Consistent-Field cycles
  • wfoptalg WaveFunction OPTimisation ALGorithm

useful:

  • dielng model DIElectric screening LeNGth
  • diemac model DIElectric MACroscopic constant
  • diemix model DIElectric MIXing factor
  • nblock_lobpcg Number of BLOCKs in the LOBPCG algorithm
  • npulayit Number of PULAY ITerations for SC mixing
  • rmm_diis Activate the RMM-DIIS eigensolver for GS calculations.
  • wfinit WaveFunctions INITialization

expert:

  • densfor_pred DENSity and FORces PREDictor
  • diecut DIElectric matrix energy CUToff
  • diegap DIElectric matrix GAP
  • dielam DIElectric matrix LAMbda
  • eshift Energy SHIFT
  • iprcel Integer for PReConditioning of ELectron response
  • isecur Integer for level of SECURity choice

Selected Input Files

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