Optimized Structural Data at the Complete Basis Set Limit via Successive Quadratic Minimizations.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Molecular modeling

Background:

• Accurate calculation of molecular structural properties is crucial in chemistry.
• Achieving the complete basis set (CBS) limit provides highly accurate theoretical results.
• Extrapolation techniques are often employed to approximate CBS properties.

Purpose of the Study:

• To introduce two novel variants of the successive quadratic minimization (SQM) method.
• To apply these SQM methods for determining structural properties at the complete basis set (CBS) limit.
• To evaluate the performance and cost-effectiveness of the proposed SQM methods.

Main Methods:

• Development and application of two successive quadratic minimization (SQM) variants: SQM and c-SQM.
• Calculation of structural parameters for molecular systems (H3+, H2O, CH2O, SH2, SO2, and water dimer) at the CBS limit.
• Comparison of results obtained with SQM methods against calculations at a lower basis set level (x2).

Main Results:

• Both SQM and c-SQM methods successfully determined CBS structural parameters that significantly improved upon raw calculations at the x2 basis set level.
• The performance of SQM methods was validated for simple molecules and the complex water dimer.
• The c-SQM method, while system-specific and potentially more costly, offered only marginal improvements over the general SQM protocol.
• The general SQM method demonstrated comparable quality to c-SQM while being more cost-effective.

Conclusions:

• The developed SQM methods are efficient and accurate for obtaining molecular structural properties at the CBS limit.
• Both SQM schemes require a small number of cycles for convergence, indicating ease of use and adaptability.
• These SQM methods can be readily integrated with existing extrapolation schemes for Hartree-Fock and correlation energies.