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In two recent papers [A. D. Becke, J. Chem. Phys. 156, 214101 (2022) and A. D. Becke, J. Chem. Phys. 157, 234102 (2022)], we compared two Kohn–Sham density functionals based on physical modeling and theory with the best density-functional power-series fits in the literature. The best error statistics reported to date for a hybrid functional on the general main-group thermochemistry, kinetics, and noncovalent interactions (GMTKN55) chemical database of Goerigk et al. [Phys. Chem. Chem. Phys. 19, 32184 (2017)] were obtained. In the present work, additional second-order perturbation-theory terms are considered. The result is a 12-parameter double-hybrid density functional with the lowest GMTKN55 WTMAD2 "weighted total mean absolute deviation" error (1.76 kcal/mol) yet seen for any hybrid or double-hybrid density-functional approximation. We call it "DH23." [ABSTRACT FROM AUTHOR]

A density functional theory exchange-correlation functional for the exploration of reaction mechanisms is proposed. This functional, denoted BMK (Boese-Martin for Kinetics), has an accuracy in the 2 kcal/mol range for transition state barriers but, unlike previous attempts at such a functional, this improved accuracy does not come at the expense of equilibrium properties. This makes it a general-purpose functional whose domain of applicability has been extended to transition states, rather than a specialized functional for kinetics. The improvement in BMK rests on the inclusion of the kinetic energy density together with a large value of the exact exchange mixing coefficient. For this functional, the kinetic energy density appears to correct “back” the excess exact exchange mixing for ground-state properties, possibly simulating variable exchange. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

When developing and assessing density functional theory methods, a finite basis set is usually employed. In most cases, however, the issue of basis set dependency is neglected. Here, we assess several basis sets and functionals. In addition, the dependency of the semiempirical fits to a given basis set for a generalized gradient approximation and a hybrid functional is investigated. The resulting functionals are then tested for other basis sets, evaluating their errors and transferability. [ABSTRACT FROM AUTHOR]

Such fifth-rung functionals approach the performance of com-posite ab initio methods such as G3 theory at a fraction of their computational cost, and with analytical derivatives avail-able. In this article, we provide a critical analysis of the varia-bles and components that maximize the accuracy of DHs. These include the selection of the exchange and correlation functionals, the coefficients of each component [density func-tional theory (DFT), exact exchange, and perturbative correla-tion in both the same spin and opposite spin terms], and the addition of an ad-hoc dispersion correction; we have termed these parametrizations "DSD-DFT" (Dispersion corrected, Spin-component scaled, Double-hybrid DFT). Somewhat surpris-ingly, the quality of DSD-DFT is only mildly dependent on the underlying DFT exchange and correlation components, with even DSD-LDA yielding respectable performance. Simple, non-empirical GGAs appear to work best, whereas meta-GGAs offer no advantage (with the notable exception of B95c). The best correlation components appear to be, in that order, B95c, P86, and PBEc, while essentially any good GGA exchange yields nearly identical results. On further validation with a wider variety of thermochemical, weak interaction, kinetic, and spectroscopic benchmarks, we find that the best functionals are, roughly in that order, DSD-PBEhB95, DSD-PBEP86, DSD-PBEPW91, and DSD-PBEPBE. In addition, DSD-PBEP86 and DSD-PBEPBE can be used without source code modifications in a wider variety of electronic structure codes. Sample job decks for several commonly used such codes are supplied as electronic Supporting Information. [ABSTRACT FROM AUTHOR]

Inearlier work [Gruzman, D.; Karton, A.; Martin, J. M. L.J. Phys. Chem. A2009, 113, 11974], we showed that conformer energiesin alkanes (and other systems) are highly dispersion-driven and thatuncorrected DFT functionals fail badly at reproducing them, whilesimple empirical dispersion corrections tend to overcorrect. To gaingreater insight into the nature of the phenomenon, we have mappedthe torsional surface of n-pentane to 10-degree resolutionat the CCSD(T)-F12 level near the basis set limit. The data obtainedhave been decomposed by order of perturbation theory, excitation level,and same-spin vs opposite-spin character. A large number of approximateelectronic structure methods have been considered, as well as severalempirical dispersion corrections. Our chief conclusions are as follows:(a) the effect of dispersion is dominated by same-spin correlation(or triplet-pair correlation, from a different perspective); (b) singlet-paircorrelation is important for the surface, but qualitatively very dissimilarto the dispersion component; (c) single and double excitations beyondthird order are essentially unimportant for this surface; (d) connectedtriple excitations do play a role but are statistically very similarto the MP2 singlet-pair correlation; (e) the form of the damping functionis crucial for good performance of empirical dispersion corrections;(f) at least in the lower-energy regions, SCS-MP2 and especially MP2.5perform very well; (g) novel spin-component scaled double hybrid functionalssuch as DSD-PBEP86-D2 acquit themselves very well for this problem. [ABSTRACT FROM AUTHOR]

The coordination number of various experimentally known Cu(I) compounds is studied using density functional theory. Various basis sets are tested, aiming to establish a reliable level for prediction of the coordination number of these and other Cu(I) complexes. It is found that most levels exhibit correct trends, namely, the bulkier ligands demonstrate larger preference for coordination of two ligands. Proper absolute values are obtained when dispersion corrections are also included in the calculations. It is concluded that the fairly small modified 6-31+G* basis set due to Pulay represents a good compromise between accuracy and efficiency, followed by Balabanov and Peterson's all-electron aug-cc-pVDZ basis set. The overall energy is decomposed into various components whose relative contribution to the overall tendency of forming a complex with a particular coordination is examined. It is shown that two opposing contributions play a major role: the interaction energy of the ligand being added and the deformation energy of the copper's coordination sphere prior to the ligand addition. The former being a stabilizing contribution, leads to higher coordination numbers while the later, a destabilizing contribution, is shown to favor lower coordination numbers. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010 [ABSTRACT FROM AUTHOR]

The previously reported reactions of cis and trans-hydroxytamoxifen drug derivatives, 1 and 2, with [Cp*Rh(L)3]2+ complexes (L = H2O, CH3OH), initially provided the kinetically controled η1-N complexes, 4(OTf, CH3OH) and 5(OTf, CH3OH), which underwent a novel, intramolecular, regioselective N-p rearrangement to provide the η1 complexes, 6 and 7. A dramatic solvent effect was also observed on the rate of this N-p rearrangement in CH3OH or CH2Cl2. Therefore, a DFT study was conducted that provided further mechanistic and thermodynamic data on this N-μ rearrangement. The preferred structures of both the η1-N and η6 complexes in the two solvents were determined, and a thorough analysis of their geometries and electronic structures has been provided. The influence of the solvent on the N-π rearrangement was studied by including the solvent both implicitly using a PCM model, and explicitly by introducing the counterion and/or the solvent molecules into the inner and outer coordination spheres of the complexes. It was shown that the triflate (OTf-) counterion was strongly bound in the inner coordination sphere of the η1-N complexes, 4(OTf) and 5(OTf), and in the outer sphere of the coordinatively saturated η1 complexes, 6 and 7, especially in non-polar media. The cleavage of the ionic Cp*Rh-OTf bond was found to be the rate-limiting step in the N-π rearrangement. The thermodynamic results suggested that the η6 complexes were more stable than the η1-N complexes in CH2Cl2and in CH3OH at elevated temperatures. The opposite relationship for the stabilities of the η1-N complexes was found in CH3OH at room temperature, thus corroborating the experimental results that the N-μ rearrangement did not occur, under these conditions. A plausible mechanistic pathway for the N-π rearrangement was proposed from our extensive DFT studies, that included several important intermediates and transition states, and provided a unique view of this novel transformation. [ABSTRACT FROM AUTHOR]

The previously reported reactions of cisand trans-hydroxytamoxifen drug derivatives, 1and 2, with [Cp*Rh(L)3]2+complexes (L = H2O, CH3OH), initially provided the kinetically controled η1-N complexes, 4(OTf, CH3OH)and 5(OTf, CH3OH), which underwent a novel, intramolecular, regioselective N–π rearrangement to provide the η6complexes, 6and 7. A dramatic solvent effect was also observed on the rate of this N–π rearrangement in CH3OH or CH2Cl2. Therefore, a DFT study was conducted that provided further mechanistic and thermodynamic data on this N–π rearrangement. The preferred structures of both the η1-N and η6complexes in the two solvents were determined, and a thorough analysis of their geometries and electronic structures has been provided. The influence of the solvent on the N–π rearrangement was studied by including the solvent both implicitly using a PCM model, and explicitly by introducing the counterion and/or the solvent molecules into the inner and outer coordination spheres of the complexes. It was shown that the triflate (OTf−) counterion was strongly bound in the inner coordination sphere of the η1-N complexes, 4(OTf)and 5(OTf), and in the outer sphere of the coordinatively saturated η6complexes, 6and 7, especially in non-polar media. The cleavage of the ionic Cp*Rh–OTf bond was found to be the rate-limiting step in the N–π rearrangement. The thermodynamic results suggested that the η6complexes were more stable than the η1-N complexes in CH2Cl2and in CH3OH at elevated temperatures. The opposite relationship for the stabilities of the η1-N complexes was found in CH3OH at room temperature, thus corroborating the experimental results that the N–π rearrangement did not occur, under these conditions. A plausible mechanistic pathway for the N–π rearrangement was proposed from our extensive DFT studies, that included several important intermediates and transition states, and provided a unique view of this novel transformation. [ABSTRACT FROM AUTHOR]

Ab initio and density functional theory (DFT) calculations were performed for obtaining fundamental vibrational frequencies of methylamine, CH3NH2, and its deuterated variants CH3ND2, CD3NH2, and CD3ND2. The calculations were carried out using the CCSD(T) coupled cluster approximation with cc-pVTZ and cc-pVQZ basis sets, and by the DFT method with the semiempirical hybrid functional B97-1 with polarization consistent pc-2 and pc-3 basis sets. Reasonable performance of the DFT harmonic and ab initio harmonic calculations was found, which improved considerably upon combination of the harmonic fundamental frequencies with anharmonic corrections from the smaller, pc-2, basis. The computed anharmonic fundamental frequencies of methylamine isotopologues agree very well with the experimental values and represent a useful tool for assignment and analysis of the dominant resonances. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008 [ABSTRACT FROM AUTHOR]

In a previous contribution, we established the suitability of density functional theory (DFT) for the calculation of molecular anharmonic force fields. In the present work, we have assessed a wide variety of basis sets and exchange-correlation functionals for harmonic and fundamental frequencies, equilibrium, and ground-state rotational constants, and thermodynamic functions beyond the rigid rotor-harmonic oscillator (RRHO) approximation. The fairly good performance of double-zeta plus polarization basis sets for frequencies results from an error compensation between basis set incompleteness and the intrinsic error of exchange-correlation functionals. Triple-zeta plus polarization basis sets are recommended, with an additional high-exponent d function on second-row atoms. All conventional hybrid generalized gradient approximation (GGA) functionals perform about equally well: high-exchange hybrid GGA and meta-GGA functionals designed for kinetics yield poor results, with the exception of of the very recently developed BMK functional, which takes a middle position along with the HCTH/407 (second-generation GGA) and TPSS (meta-GGA) functionals. Second-order Møller–Plesset perturbation theory (MP2) performs similarly to these functionals but is inferior to hybrid GGAs such as B3LYP and B97-1. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [ABSTRACT FROM AUTHOR]

The very good performance of modern density functional theory for molecular geometries and harmonic vibrational frequencies has been well established. We investigate the performance of density functional theory (DFT) for quartic force fields, vibrational anharmonicity and rotation–vibration coupling constants, and thermodynamic functions beyond the RRHO (rigid rotor–harmonic oscillator) approximation of a number of small polyatomic molecules. Convergence in terms of basis set, integration grid and the numerical step size for determining the quartic force field by using central differences of analytical second derivatives has been investigated, as well as the performance of various exchange-correlation functionals. DFT is found to offer a cost-effective approach with manageable scalability for obtaining anharmonic molecular properties, and particularly as a source for anharmonic zero-point and thermal corrections for use in conjunction with benchmark ab initio thermochemistry methods. [ABSTRACT FROM AUTHOR]

The Suzuki–Miyaura cross-coupling reaction with the SPhos ligand was studied with DFT and analyzed within the energetic span model. With this information, we designed a modification to the SPhos (the “InPhos”), which theoretically corrects the deficiencies of the prior ligand. [ABSTRACT FROM AUTHOR]

Investigates the mechanical details of the cycloaddition reactions of metallabenzenes complexes using density functional theory. Formation of cyclopentadienyl (Cp) complexes; Coupling of two aromatic metals involved in the Cp formation; Classification of the reaction as a carbene migratory insertion using density functional theory.

The mechanistic details of the Meerwein-Schmidt-Ponndorf-Verley (MSPV) reduction of ketones to the corresponding alcohols were investigated both experimentally and computationally. Density functional theory (DFT) was used to assess the energetics of several proposed pathways (direct hydrogen transfer, hydridic, and radical). Our results demonstrate that a direct hydrogen transfer mechanism involving a concerted six-membered ring transition state is the most favorable pathway for all calculated systems starting from a small model system and concluding with the experimentally investigated BlNOLate/AI/iPrOH/MePhC=O system. Experimental values for the activation parameters of acetophenone reduction using the BlNOLate/Al/iPrOH system (δG# = 21.8 kcal/mol, δH# = 18.5 kcal/mol, δS# = -11.7 au) were determined on the basis of kinetic investigation of the reaction and are in good agreement with the computational findings for this system. Calculated and experimental kinetic isotope effects support the concerted mechanism. [ABSTRACT FROM AUTHOR]