Regular Article

Theoretical Chemistry Accounts

, Volume 130, Issue 4, pp 633-644

An improved algorithm for the normalized elimination of the small-component method

  • Wenli ZouAffiliated withDepartment of Chemistry, Southern Methodist University
  • , Michael FilatovAffiliated withUniversity of Groningen
  • , Dieter CremerAffiliated withDepartment of Chemistry, Southern Methodist University Email author 

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Abstract

A new algorithm for the iterative solution of the normalized elimination of the small component (NESC) method is presented that is less costly than previous algorithms and that is based on (1) solving the NESC equations for the uncontracted rather than contracted basis (“First-Diagonalize-then-Contract”), (2) a new iterative procedure for obtaining the NESC Hamiltonian (“iterative TU algorithm”), (3) the renormalization scheme connected to the picture change, and (4) a finite nucleus model with a Gaussian charge distribution. The accuracy of NESC energies, which match those of 4-component Dirac calculations, is demonstrated. Test calculations with CCSD(T), DFT, and large basis sets including high angular momentum basis functions (f,g,h,i) are presented to prove the general applicability of the new NESC algorithm. Comparison with other algorithms of solving the NESC equations are shortly discussed and time savings are presented.

Keywords

Normalized Elimination of the Small Component (NESC) Exact quasi-relativistic methods Picture change Finite nucleus model