Molecular core-valence correlation effects involving the post-d elements Ga-Rn: benchmarks and new...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate quantum chemical calculations require appropriate basis sets to describe electron correlation.
• Previous basis sets (cc-pVXZ-PP) were limited to valence nsp electron correlation for post-d elements.
• Outer-core (n-1)spd electron correlation effects were not adequately addressed for heavier post-d elements.

Purpose of the Study:

• To develop new correlation consistent basis sets (cc-pwCVXZ-PP) for the accurate treatment of outer-core (n-1)spd electron correlation.
• To investigate the impact of outer-core electron correlation on the properties of post-d elements (Ga-Rn).
• To assess the reliability of small-core relativistic pseudopotentials (PPs) in conjunction with these new basis sets.

Main Methods:

• Development of new correlation consistent basis sets, cc-pwCVXZ-PP (X=D,T,Q,5), building upon cc-pVXZ-PP sets.
• Utilizing accurate small-core relativistic pseudopotentials (PPs) designed for valence nsp correlation.
• Performing benchmark coupled cluster calculations to evaluate core-valence correlation effects on molecular properties.

Main Results:

• The correlation of (n-1)d electrons significantly impacts dissociation energies (e.g., 1.5-3.2 kcal/mol for Group 13 diatomics), bond lengths, and harmonic frequencies.
• Outer-core (n-1)p electron correlation is less significant than (n-1)d but more important than (n-1)s correlation.
• Additional tight functions for Hartree-Fock and valence sp correlation show substantial effects, particularly for post-4d and post-5d elements.

Conclusions:

• The developed cc-pwCVXZ-PP basis sets provide a robust framework for including crucial outer-core electron correlation in post-d elements.
• The inclusion of (n-1)d electron correlation is essential for accurate predictions of molecular properties for these elements.
• Pseudopotential approximation errors are minimal when compared to all-electron Douglas-Kroll-Hess calculations.