Basis Set Superposition Errors Are Partly Basis Set Imbalances.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Electronic structure theory

Background:

• Electronic structure methods are crucial for calculating fragment interaction energies.
• Medium-sized atom-centered basis sets commonly lead to systematic overestimation of these energies.
• The prevailing interpretation attributes this overestimation to basis set superposition errors.

Purpose of the Study:

• To investigate the cause of systematic errors in fragment interaction energy calculations.
• To explore the role of basis set imbalance in these errors.
• To evaluate the effectiveness of explicit basis set optimization in mitigating these errors.

Main Methods:

• Utilizing electronic structure methods with medium-sized atom-centered basis sets.
• Analyzing cases where interaction energies are underestimated, challenging the standard basis set superposition error interpretation.
• Implementing explicit optimization of basis sets for individual molecular structures.

Main Results:

• Observed underestimation of interaction energies in some cases, indicating basis set imbalance as a contributing factor.
• Explicit optimization of basis sets for each structure was performed.
• This optimization significantly reduced the overestimation attributed to basis set superposition error.

Conclusions:

• Basis set imbalance, not solely basis set completeness, contributes to errors in fragment interaction energy calculations.
• Explicit basis set optimization is an effective strategy to correct for basis set imbalance.
• The findings refine the understanding and correction of basis set superposition errors in computational chemistry.