Extending the Applicability of the Semi-experimental Approach by Means of “Template Molecule” and “Linear Regression” Models on Top of DFT Computations

Abstract

The accurate determination of equilibrium structures for isolated molecules plays a central role in the evaluation and interpretation of stereoelectronic, thermodynamic, and spectroscopic properties. For small semi-rigid systems, state-of-the-art quantum-chemical computations can rival the most sophisticated experimental results. For larger molecules, cheaper yet accurate approaches need to be defined. The double-hybrid rev-DSD-PBEP86 functional already delivers remarkable results that can be further improved by means of a “Lego brick” model. This is based on the idea that a molecular system can be seen as formed by different fragments (the “Lego bricks”), whose accurate semi-experimental (SE) equilibrium geometries are available. The template molecule (TM) approach can be used to account for the modifications occurring when going from the isolated fragment to the molecular system under investigation, with the linear regression (LR) model employed to correct the linkage between the different fragments. The resulting TM-SE_LR approach has been tested with respect to available SE equilibrium structures and rotational constants. Indeed, the latter parameters straightforwardly depend on the equilibrium geometry of the system under consideration. The main outcome of our study is the reliability, robustness, and accuracy of this novel approach. The molecular systems considered for benchmarking the TM-SE_LR scheme are those formally issued from addition/elimination reactions of nucleophilic unsaturated radicals (e.g., CN, C2H, and phenyl) to alkenes, imines, and aldehydes, whose rotational spectra have been investigated, but accurate structural determinations are not yet available.

Exploiting the “Lego brick” approach to predict accurate molecular structures of PAHs and PANHs

“…31,32 In ref. 27, the resulting model has been denoted as the TM-SE_LR approach. Here, we refer to it simply as TM+LR (only TM if LR is not applied).…”

“…To obtain accurate equilibrium structures while retaining a feasible computational cost, a possible way-out is offered by the so-called “Lego brick” approach. 27 This is based on the idea that medium-to-large systems can be seen as formed by different fragments ( i.e. , the “Lego bricks”), whose accurate equilibrium geometries are available.…”

“…The reliability, robustness, and accuracy of this model have been demonstrated in ref. 27. In such an investigation, the SE structures of two fragments were used to template the geometrical parameters of larger systems obtained using a double-hybrid density functional in conjunction with a partially augmented triple-zeta basis set.…”

Toward Accurate Formation Routes of Complex Organic Molecules in the Interstellar Medium: The Paradigmatic Cases of Acrylonitrile and Cyanomethanimine

“…In this connection, the B2PLYP-D3/ maug-cc-pVTZ model (Grimme, 2006;Papajak et al, 2009) employed in our earlier studies has recently been replaced by the rev-DSD-PBEP86 functional (Santra et al, 2019) in conjunction with the jun-cc-pVTZ (Papajak et al, 2011) basis set (such a functional-basis combination is shortly denoted as rev-DSD in the following), which usually delivers improved results (with respect to the former) for transition states and non-covalent complexes without reducing the accuracy of other parameters. When more accurate geometries are sought (especially in connection with spectroscopic properties or intermolecular distances of pre-reactive complexes), more accurate quantum-chemical approaches (vide infra) or a "LEGO bricks" approach can be employed (Ceselin et al, 2021;Melli et al, 2021).…”

Benefits of Range-Separated Hybrid and Double-Hybrid Functionals for a Large and Diverse Data Set of Reaction Energies and Barrier Heights

“…(We note in passing that the analytical first 43 and second 44 derivatives for DHs are available in the literature, not just in the gas phase but also in continuum solvents. 45 This is of interest not merely for computational spectroscopy, see refs ( 46 and 47 ) and references therein, but also will greatly facilitate locating accurate transition state structures.)…”