Automated incremental scheme for explicitly correlated methods.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Electronic structure theory

Background:

• Accurate calculation of molecular energies is crucial for predicting chemical reaction outcomes.
• Traditional methods can be computationally expensive, necessitating efficient algorithms.
• Explicitly correlated methods like F12 improve convergence but require careful implementation.

Purpose of the Study:

• To present an automated incremental scheme for calculating MP2-F12 and CCSD(F12) energies.
• To assess the numerical accuracy of this automated approach for chemical reactions.
• To determine the required order of expansion for achieving chemical accuracy (1 kcal/mol).

Main Methods:

• Development and implementation of an automated incremental scheme.
• Testing on 15 chemical reactions using a worst-case scenario (single orbital one-site domains).
• Analysis of results using maximum absolute deviation, mean absolute error, and root mean square error.

Main Results:

• MP2 reaction energies achieve 1 kcal/mol accuracy at the third order of the expansion.
• F12 corrections demonstrate sufficient accuracy at the second order.
• CCSD(F12) calculations reach 1 kcal/mol accuracy at the fourth order of the expansion.

Conclusions:

• The automated incremental scheme provides an accurate and efficient method for computing MP2-F12 and CCSD(F12) energies.
• The study establishes the necessary orders of expansion for achieving chemical accuracy in these methods.
• This work facilitates more reliable computational predictions in quantum chemistry.