Reliable Electronic Structure Calculations for Heavy Element Chemistry: Molecules Containing Actinides, Lanthanides, and Transition Metals: Relativistic Pseudopotentionals in Accurate ab Initio Molecular Electron Structure Calculations

Relativistic Pseudopotentionals (RPPs) are a new form of relativistic effective core potentials (RECP) that are based on extending the usual two-space representation of atomic electrons (core and valence) to three spaces: core, outer core, and valence. The RPP has embedded within it the so-called small-core RECP, viz., one that relegates the outer core electrons to the valence space. The RPP is ultimately specified completely only at runtime and is specific to the molecular environment (geometry and electronic state). Only the smallest number of molecular valence electrons need to be treated explicitly, and can be used in any treatment of the electronic structure including DFT, CI (configuration interaction), MBPT (many body perturbation theory), coupled cluster theory (CCSD/CCSD(T)), etc. Furthermore, the one-particle basis set (orbitals or spinors) need only be sufficiently flexible to represent the valence electrons no core or outer core basis functions are required. As the RPP formalism has only recently been developed, its implementation and application are key thrusts of this project. The enormous reduction in computational effort over all-electron and standard RECP approaches, coupled with the inclusion of relativistic and core/valence polarization and correlation phenomena, are principal advantages to using RPPs to study heavy atom complexes.