Post-Semiempirical Methods for Thermochemistry

Addressing complex challenges in chemistry and materials science requires improved computational modeling. The Roothaan-Hall equations enable high accuracy but create a critical bottleneck that limits efficiency in large-scale computational quantum chemistry, particularly for thermochemistry. Density functional theory (DFT) methods are highly accurate but remain too costly for systems larger than a few hundred atoms. Semiempirical quantum mechanical (SQM) models are orders of magnitude faster and applicable to thousands of atoms but lack accuracy. This poster introduces a novel strategy to overcome the Roothaan-Hall bottleneck by breaking down the challenging task of SQM development into smaller manageable components. We highlight current progress in developing a new and timely SQM that achieves DFT-level accuracy at SQM computational cost and offers additional chemical insight.