An examination of intrinsic errors in electronic structure methods using the Environmental Molecular Sciences Laboratory computational results database and the Gaussian-2 set

Abstract

The Gaussian-2 ͑G2͒ collection of atoms and molecules has been studied with Hartree-Fock and correlated levels of theory, ranging from second-order perturbation theory to coupled cluster theory with noniterative inclusion of triple excitations. By exploiting the systematic convergence properties of the correlation consistent family of basis sets, complete basis set limits were estimated for a large number of the G2 energetic properties. Deviations with respect to experimentally derived energy differences corresponding to rigid molecules were obtained for 15 basis set/method combinations, as well as the estimated complete basis set limit. The latter values are necessary for establishing the intrinsic error for each method. In order to perform this analysis, the information generated in the present study was combined with the results of many previous benchmark studies in an electronic database, where it is available for use by other software tools. Such tools can assist users of electronic structure codes in making appropriate basis set and method choices that will increase the likelihood of achieving their accuracy goals without wasteful expenditures of computer resources.

The Molecular Structures and Energetics of Cl2CO, ClCO, Br2CO, and BrCO

“…(All bond energies calculated at 0 K. [2][3][4] Our laboratory has recently been developing a composite theoretical approach that is intended to reliably predict a variety of thermodynamic quantities, including heats of formation, without recourse to empirical parameters. 1,[5][6][7][8][9][10][11][12][13] As described below, our approach starts with existing, reliable thermodynamic values (obtained from either experiment or theory). Missing pieces of information are then computed by using high-level ab initio electronic structure methods, such as coupled cluster methods including single, double, and connected triple excitations, with the latter being handled perturbatively.…”

“…Application of this method to a group of 73 molecules, many of which were taken from the G2 and G2/97 test set, yielded a mean absolute deviation with respect to experiment of 0.7 to 0.8 kcal/mol. 9,12 Computational Approach For the 1-particle expansion, we use the correlation-consistent (cc) basis sets from Dunning and co-workers 17-21 because of the regularity with which they approach the CBS limit. We have previously found that convergence of the energy is improved if the cc basis sets are augmented by an additional shell of diffuse functions, especially for polar molecules.…”

“…[14][15][16] This method, known conventionally as CCSD(T), is capable of recovering a large fraction of the correlation energy for molecules that can qualitatively be described by a single electronic configuration. 9,12 To further reduce the magnitude of the finite basis set (1-particle) error, the CCSD(T) energies are extrapolated to the complete basis set (CBS) limit. To improve the agreement with experiment, corrections for core/valence correlation, atomic spin-orbit effects, molecular scalar relativistic effects, and the remaining correlation energy are required.…”

Validação computacional de métodos compostos no estudo de propriedades moleculares

“…3 Juntos, esses avanços, levaram a avaliações mais precisas de diversas propriedades moleculares, em especial relacionadas a grandezas termoquímicas. [4][5][6][7][8][9][10] Mesmo tendo em mãos métodos sofisticados e funções de base extensas para descrever qualquer sistema eletrônico, a realização prática de cálculos que envolvam um grande número de partículas ainda é uma tarefa dispendiosa computacionalmente. Algumas estratégias têm tido sucesso e tornado possível a abordagem precisa de sistemas químicos relativamente grandes.…”

Theoretical study of thermochemical properties using composite methods adapted to ONIOM

“…[1][2][3][4][5][6][7][8][9] However, practical calculations containing many particles become a task that requires a very high computational cost. 10 Some strategies have been successful, making it possible to study large systems, highlighting the composite methods [11][12][13][14][15][16][17][18][19] and the ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) method.…”