Transferable Quasiparticle Correlation, Subtractive Multireference Embedding for Biradicaloid Ozone, and Retarded Casimir–Polder Dispersion in Multi-Electron Systems
Abstract
Computing accurate electron correlation across closed-shell polyatomics, multireference biradicaloids, and non-covalent van der Waals complexes represents a fundamental challenge in quantum chemistry. In this work, we investigate a transferable range-separated quasiparticle framework for molecular electronic structure and dispersion. First, for closed-shell polyatomics (CH4, NH3, H2O, CO2), the range-separated quasiparticle Dyson denominator parameters (mu = 0.50, alpha_sr = 1.35 a_0^-1, lambda_mu = 0.38) established on two-electron calibration benchmarks are transferred without molecule-specific re-optimization to 10- to 24-electron molecules, achieving an out-of-sample correlation energy Mean Absolute Error (MAE) of 5.809 mHa vs. CCSD(T) across 6-31G* and cc-pVDZ basis sets (a 2.69x improvement over MP2 and 2.04x over CCSD). Second, for the multireference biradicaloid ozone molecule (O3, 1 1A_1), subtractive CASCI embedding accurately captures static correlation across the 11-point bending potential energy curve (theta_OOO in [105 deg, 130 deg], MAE 1.137 mHa), predicting an equilibrium bond angle of 116.755 deg (experiment 116.78 deg) and resolving the Hartree-Fock permanent dipole anomaly (0.5526 D vs. experiment 0.5337 D, where RHF diverges to 0.7937 D). Finally, we evaluate long-range non-covalent dispersion by combining Time-Dependent Hartree-Fock (TDHF) dynamic polarizabilities with a fractional memory retardation kernel and rational Becke-Johnson damping. We demonstrate that the memory kernel strictly screens dynamic polarizability relative to unretarded TDHF, with effective retardation coupling increasing systematically with monomer polarizability (0.02 a.u. for He, 0.05 a.u. for H2, and 0.08 a.u. for C2H4), yielding counterpoise-corrected binding curves for He2, (H2)2, and parallel-displaced pi-stacked ethylene dimers with MAEs of 0.0155, 0.0421, and 0.1336 kcal/mol vs. CCSD(T). Listing 1
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BibTeX
@misc{singh2026transferable,
title = {{Transferable Quasiparticle Correlation, Subtractive Multireference Embedding for Biradicaloid Ozone, and Retarded Casimir–Polder Dispersion in Multi-Electron Systems}},
author = {Mehardeep Singh},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010849/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010849/v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - Transferable Quasiparticle Correlation, Subtractive Multireference Embedding for Biradicaloid Ozone, and Retarded Casimir–Polder Dispersion in Multi-Electron Systems
AU - Mehardeep Singh
PY - 2026
DA - 2026/10/22
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010849/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010849/v1
AB - Computing accurate electron correlation across closed-shell polyatomics, multireference biradicaloids, and non-covalent van der Waals complexes represents a fundamental challenge in quantum chemistry. In this work, we investigate a transferable range-separated quasiparticle framework for molecular electronic structure and dispersion. First, for closed-shell polyatomics (CH4, NH3, H2O, CO2), the range-separated quasiparticle Dyson denominator parameters (mu = 0.50, alpha_sr = 1.35 a_0^-1, lambda_mu = 0.38) established on two-electron calibration benchmarks are transferred without molecule-specific re-optimization to 10- to 24-electron molecules, achieving an out-of-sample correlation energy Mean Absolute Error (MAE) of 5.809 mHa vs. CCSD(T) across 6-31G* and cc-pVDZ basis sets (a 2.69x improvement over MP2 and 2.04x over CCSD). Second, for the multireference biradicaloid ozone molecule (O3, 1 1A_1), subtractive CASCI embedding accurately captures static correlation across the 11-point bending potential energy curve (theta_OOO in [105 deg, 130 deg], MAE 1.137 mHa), predicting an equilibrium bond angle of 116.755 deg (experiment 116.78 deg) and resolving the Hartree-Fock permanent dipole anomaly (0.5526 D vs. experiment 0.5337 D, where RHF diverges to 0.7937 D). Finally, we evaluate long-range non-covalent dispersion by combining Time-Dependent Hartree-Fock (TDHF) dynamic polarizabilities with a fractional memory retardation kernel and rational Becke-Johnson damping. We demonstrate that the memory kernel strictly screens dynamic polarizability relative to unretarded TDHF, with effective retardation coupling increasing systematically with monomer polarizability (0.02 a.u. for He, 0.05 a.u. for H2, and 0.08 a.u. for C2H4), yielding counterpoise-corrected binding curves for He2, (H2)2, and parallel-displaced pi-stacked ethylene dimers with MAEs of 0.0155, 0.0421, and 0.1336 kcal/mol vs. CCSD(T). Listing 1
ER -