Relativistic effects determined using the Douglas-Kroll contracted basis sets and correlation consistent basis sets...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate prediction of molecular properties is crucial for understanding chemical behavior.
• Scalar relativistic effects become increasingly important for heavier elements, influencing electronic structure and reactivity.
• Previous studies have focused on lighter elements, necessitating investigation into third-row systems.

Purpose of the Study:

• To investigate the impact of scalar relativistic corrections on the energetic and structural properties of small molecules containing third-row atoms (Gallium to Krypton).
• To compare relativistic and nonrelativistic computational results for key molecular properties.
• To assess the accuracy of the coupled cluster approximation with single, double, and quasiperturbative triple excitations [CCSD(T)] in describing these systems.

Main Methods:

• Employed the coupled cluster approximation with single, double, and quasiperturbative triple excitations [CCSD(T)].
• Utilized Douglas-Kroll contracted correlation consistent basis sets [cc-pVnZ-DK] and relativistic pseudopotentials with correlation consistent polarized valence basis sets [cc-pVnZ-PP, aug-cc-pVnZ-PP].
• Calculated atomization energies, ionization energies, electron affinities, and proton affinities for molecules from the Gaussian-2 extended test set for third-row atoms.
• Extrapolated energies to the complete basis set limit using several schemes.

Main Results:

• Scalar relativistic corrections were found to significantly alter energetic properties such as atomization energies, ionization energies, electron affinities, and proton affinities.
• Structural parameters also showed noticeable changes due to relativistic effects.
• Comparison with nonrelativistic results highlighted the necessity of including relativistic treatments for accurate predictions of third-row molecular properties.

Conclusions:

• Scalar relativistic effects play a critical role in the accurate theoretical description of molecules containing third-row elements.
• The CCSD(T) method in conjunction with appropriate relativistic basis sets provides reliable predictions for these systems.
• This work provides a benchmark for future computational studies involving heavier main-group elements.