Accurate Atomic Correlation and Total Energies for Correlation Consistent Effective Core Potentials.

Area of Science:

• Quantum Chemistry
• Condensed Matter Physics
• Computational Physics

Background:

• Effective core potentials (ECPs) are crucial for reducing computational cost in electronic structure calculations.
• Previous ECPs lacked the accuracy required for high-precision studies.
• Full many-body approaches offer a path to more accurate ECPs.

Purpose of the Study:

• To provide benchmark total energy calculations for recently developed correlation consistent effective core potentials (ccECPs).
• To establish a reliable reference for future high-accuracy quantum chemistry and condensed matter physics research.
• To assess the accuracy and transferability of ccECPs across various electronic structure methods.

Main Methods:

• Configuration Interaction (CI), Coupled-Cluster (CC), and Quantum Monte Carlo (QMC) calculations were employed.
• Full CI/CCSD(T)/CCSDT(Q) calculations were performed using cc-pVnZ basis sets up to n=6.
• Complete basis set limits were estimated, and fixed-node diffusion Monte Carlo energies were calculated.

Main Results:

• Total energies for ccECPs were calculated with high accuracy (≈1-10 mHa for K-Zn, ≈0.1-0.3 mHa for others).
• Achieved accuracy is within ~1% of ccECP total correlation energies.
• Kinetic energies and fixed-node biases in QMC were also estimated.

Conclusions:

• The presented benchmark calculations validate the accuracy of ccECPs.
• These results serve as a crucial reference for correlated wave function and stochastic methods.
• The study facilitates more reliable and accurate computational studies in chemistry and physics.