On the accuracy limits of orbital expansion methods: Explicit effects of k-functions on atomic and molecular energiesReportar como inadecuado


On the accuracy limits of orbital expansion methods: Explicit effects of k-functions on atomic and molecular energies


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For selected first- and second-row atoms, correlation-optimized Gaussian k functions have been determined and used in the construction of septuple-ζ basis sets for the correlation-consistent cc-pVXZ and aug-cc-pVXZ series. Restricted Hartree–Fock RHF and second-order Møller–Plesset MP₂ total and pair energies were computed for H, N, O, F, S, H₂ , N₂ , HF, H₂ O, and H₂ O₂ to demonstrate the consistency of the new septuple-ζ basis sets as extensions of the established aug-cc-pVXZ series. The pV7Z and aug-pV7Z sets were then employed in numerous extrapolation schemes on the test species to probe the accuracy limits of the conventional MP₂ method vis-à-vis explicitly correlated MP2 -R12 -A benchmarks. For singlet, triplet pairs, X+½⁻n functional forms with n = 3, 5 proved best for extrapolations. The mean abs. relative error, std. dev. among the 73 singlet pair energies in the dataset is 1.96%, 0.54% and 1.7₂ %, 0.51% for explicit computations with the pV7Z and aug-pV7Z basis sets, respectively, but only 0.07%, 0.09% after two-point, 6Z-7Z extrapolations with the X+½⁻³ form. The effects of k functions on molecular relative energies were examined by application of the septuple-ζ basis sets to the barrier to linearity and the dimerization energy of water. In the former case, an inherent uncertainty in basis set extrapolations persists which is comparable in size to the error ≈ 20 cm⁻¹ in explicit aug-pV7Z computations, revealing fundamental limits of orbital expansion methods in the domain of subchemical accuracy 0.1 kcal mol ⁻¹.



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Autor: Valeev, Edward F. - Allen, Wesley D. - Hernandez, Rigoberto - Sherrill, C. David - Schaefer, Henry F. - -

Fuente: https://smartech.gatech.edu/



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