A new generation of effective core potentials from correlated calculations: 2nd row elements

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Atomic and Molecular Physics

Background:

• Effective core potentials (ECPs) are crucial for simplifying electronic structure calculations.
• Correlation consistent ECPs (ccECPs) are designed for high accuracy, particularly in explicitly correlated methods.
• Previous ccECPs were derived from many-body approaches, focusing on valence states and molecular properties.

Purpose of the Study:

• To extend the development of ccECPs to 2nd-row elements.
• To investigate construction aspects for high-accuracy ccECPs with 3s, 3p valence space (Ne-core).
• To develop an alternative He-core ccECP for enhanced accuracy across the 2nd row.

Main Methods:

• Derivation of ccECPs based on reproducing excitation energies and achieving near-isospectrality.
• Refinement using binding curves of dimer molecules for improved transferability.
• Application to 2nd-row elements (e.g., Al, Si) with Ne-core and He-core constructions.

Main Results:

• New Ne-core ccECPs show accurate low-lying atomic excitations (≈0.03 eV) and equilibrium molecular bonds (≈3 mÅ).
• Limitations observed for Al and Si oxide molecules at short bond lengths for both new and existing ECPs.
• He-core ccECPs demonstrate high uniform accuracy with typical discrepancies of ≈0.01 eV or smaller.

Conclusions:

• The developed ccECPs offer a systematic balance between atomic spectra accuracy and molecular bond transferability.
• The He-core ccECPs provide a valuable option for highly accurate calculations on 2nd-row elements.
• Further investigation into limitations at short bond lengths for specific molecules is warranted.