Advanced Charge Extended Hückel (CEH) Model and a Consistent Adaptive Minimal Basis Set for the Elements Z=1-103

28 October 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

The Charge Extended Hückel (CEH) model, initially introduced for adaptive atomic orbital (AO) basis set construction (J. Chem. Phys. 159, 164108 (2023)), has been significantly revised to enhance accuracy and robustness, particularly in challenging electronic situations. This revision includes an extension towards f-elements, covering actinoids with their f-electrons in the valence space. We present a novel non-iterative approximation for the electrostatic contribution to the effective Fock matrix, which substantially improves performance in polar or charged systems. Additionally, the training dataset for elements Z = 1-103 has been expanded to encompass even more chemically diverse reference molecules as well as dipole moments and shell populations in addition to atomic charges. It includes a greater variety of "mindless" molecules (MLMs) as well as more complex electronic structures through open-shell and highly charged species. The revised method achieves mean absolute errors for atomic charges q of approximately 0.02 e- for randomly selected (mostly organic) molecules and 0.09 e- for MLMs, outperforming both classical charge models and established tight-binding methods. Furthermore, the revised CEH model has been validated through density functional theory calculations with the updated adaptive q-vSZP AO basis set on common thermochemical databases. Consistent with the extension of the CEH model, q-vSZP has also been variationally optimized and tested for elements Z = 58-71 and 87-103. The original versions of both CEH and q-vSZP are now considered deprecated.

Keywords

DFT
Basis sets
SQM
EHT

Supplementary materials

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Electronic Supporting Information
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Electronic Supporting Information for the manuscript "Advanced Charge Extended Hückel (CEH) Model and a Consistent Adaptive Minimal Basis Set for the Elements Z=1-103". Theoretical details of the CEH model, additional information on the random molecule selection and analysis, the q-vSZP basis set and corresponding ECPs in a machine-readable format, and details on the ”mindless” molecule generation and benchmark data are provided in the electronic SI. Additionally, molecular structures and corresponding charges for randomly selected molecules; actinide complexes, and ”mindless” molecules; CEH-v2 and EEQ charge for the LFER correlation; tabulated results for the U2C@C80 association energy; detailed GMTKN55 benchmark data; and relevant scripts for generation of the most important figures are contained in "assets/SI-qvSZP-v2" within the q-vSZP GitHub repository (https://github.com/grimme-lab/qvSZP).
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