Semi-Experimental Equilibrium Structure Determinations by Employing B3LYP/SNSD Anharmonic Force Fields: Validation and Application to Semirigid Organic Molecules

Abstract

This work aims at extending the semi-experimental (SE) approach for deriving accurate equilibrium structures to large molecular systems of organic and biological interest. SE equilibrium structures are derived by a least-squares fit of the structural parameters to the experimental ground-state rotational constants of several isotopic species corrected by vibrational contributions computed by quantum mechanical (QM) methods. A systematic benchmark study on 21 small molecules (CCse set) is carried out to evaluate the performance of hybrid density functionals (in particular B3LYP) in the derivation of vibrational corrections to rotational constants. The resulting SE equilibrium structures show a very good agreement with the corresponding geometries obtained employing post-Hartree-Fock vibrational corrections. The use of B3LYP in conjunction with the double-ζ SNSD basis set strongly reduces the computational costs, thus allowing for the evaluation of accurate SE equilibrium structures for medium-sized molecular systems. On these grounds, an additional set of 26 SE equilibrium structures including the most common organic moieties has been set up by collecting the most accurate geometries available in the literature together with new determinations from the present work. The overall set of 47 SE equilibrium structures determined using B3LYP/SNSD vibrational corrections (B3se set) provides a high quality benchmark for validating the structural predictions of other experimental and/or computational approaches. Finally, we present a new strategy (referred to as the template approach) to deal with the cases for which it is not possible to fit all geometrical parameters due to the lack of experimental data.

Aiming at an accurate prediction of vibrational and electronic spectra for medium‐to‐large molecules: An overview

“…The equilibrium structures have been compared with the so‐called semiexperimental (SE) equilibrium geometry ( ), accurate within 0.001 Å and 0.1 degrees for bond lengths and angles, respectively, taken from a database providing geometries for a large number of small and medium‐size molecules . Moreover, the accuracy of the theoretical vibrationally averaged structures have been evaluated by comparing the theoretical and experimentally measured rotational constants ( B 0 ) .…”

“… Accuracy of thiophene's structural parameters computed with different DFT functionals, equilibrium structures (bond lengths in Å and angles in degrees) compared with the best estimated semiexperimental data ( ) from references and and the theoretical rotational constants ( B 0 , in %) compared with experimental data…”

Quadratic integrand double-hybrid made spin-component-scaled

“…More information about the properties included in the GMTKN30 database is given in Table SI and SII of the supplementary material. 40 Molecular structures included into the B3se47 dataset 41 were fully optimized with the Dunningaugmented triple-ζ basis set, and the performances of the DHs were judged according the distance matrix deviations as recently described in Ref. 22.…”

“…Its performance is now tested on a large variety of short-and long-range energetic properties included into the extended GMTKN30 benchmark set, 35 and on molecular structure properties considered into the B3se47 dataset. 41 Figure 3 reports the MADs for these series of properties for the QIDH and SOS1-QIDH models for three different values of the a s parameter sampled around the minimum of the blue curve represented in Figure 2 (see Table SII in the supplementary material for numerical details 40 ).…”

A full‐pivoting algorithm for the Cholesky decomposition of two‐electron repulsion and spin‐orbit coupling integrals

“…The geometries for benzene and cis ‐acrolein come from the CCse set of geometries reported in Ref. , while the geometry for Dy complex from its crystallographic structure, reported in Ref. .…”