Abstract
Various molecular parameters in quantum chemistry could be computed as derivatives of energy over different arguments. Unfortunately, it is quite complicated to obtain analytical expression for characteristics that are of interest in the framework of methods that account electron correlation. Especially it relates to the coupled cluster (CC) theory. In such cases, numerical differentiation comes to rescue. This approach, like any other numerical method has empirical parameters and restrictions that require investigation. Current work is called to clarify the details of Finite-Field method usage for high-order derivatives calculation in CC approaches. General approach to the parameter choice and corresponding recommendations about numerical steadiness verification are proposed. As an example of Finite-Field approach implementation characterization of optical properties of fullerene passing process through the aperture of carbon nanotorus is given.
Highlights
IntroductionThe bases of Finite-Field method (FF) as an approach for calculations of different molecular parameters (e.g. electro-optical properties, shielding constants, etc.) were founded in the end of 1960th [1]
The bases of Finite-Field method (FF) as an approach for calculations of different molecular parameters were founded in the end of 1960th [1]
First calculations for di- and triatomic molecules revealed that Hartree-Fock method (HF) results are in significant divergence with those obtained in more accurate methods
Summary
The bases of Finite-Field method (FF) as an approach for calculations of different molecular parameters (e.g. electro-optical properties, shielding constants, etc.) were founded in the end of 1960th [1]. Its use was restricted by employing the Hartree-Fock method (HF) as a quantum-chemistry approach for in-field system energy calculation. As computational practice shows [8], account of the EC effects plays essentially important role for π-conjugated systems (especially when high-order susceptibilities are of interest). Employed density functional theory (DFT) [9] and second-order many-body perturbation theory (MBPT2) [10] roughly account these effects and for the series of systems are unable to estimate the whole set of desired properties with proper accuracy [8]. Implemented approach uses the PPP (Pariser-Parr-Pople) parameterization for π-electron variant of coupled clusters (CC) singles and doubles (CCSD) method with covalently unbonded ethylene molecules as reference state (cue-CCSD). [12,13,14]
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