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Multiconfiguration pair-density functional (MC-PDFT) theory provides an economical way to calculate the ground-state and excited-state energetics of strongly correlated systems. The energy is calculated from the kinetic energy, density, and on-top pair-density of a multiconfiguration wave function as the sum of kinetic energy, classical Coulomb energy, and on-top density functional energy. We have usually found good results with the translated Perdew–Burke–Ernzerhof (tPBE) on-top density functional, and in this article, we examine whether the results can be systematically improved by introducing scaling constants into the exchange and correlation terms. We find that only a small improvement is possible for electronic excitation energies and that no improvement is possible for bond energies. [ABSTRACT FROM AUTHOR]

This work examines the question of how a Hubbard U correction to a local exchange–correlation functional compares with adding Hartree–Fock exchange to a local functional for both solid-state and molecular properties. We compute a solid-state property, namely the band gap, and thermochemical molecular properties, in particular, main-group bond energies, transition metal–ligand bond energies, and barrier heights, to elucidate whether the DFT+U method mimics hybrid DFT. We find that a calculation with a Hubbard U correction may or may not mimic a hybrid functional—depending on the atom, the subshell, and the property to which it is applied. For band gaps, we find that adding a Hubbard U correction to the valence d orbitals of transition metals increases the band gap, which thereby gets closer to the experimental value, while adding a Hubbard U correction to valence s or p orbitals of main-group elements need not always increase the band gap. For molecular thermochemistry, we find that adding a Hubbard U correction to a local density functional need not have the same effect as adding Hartree–Fock exchange to a local density functional. For example when compared to a DFT calculation with a local exchange-correlation functional, hybrid DFT increases the barrier height in all cases, but DFT+U does not always increase the barrier height. For the band gaps of transition metal monoxides, the Hubbard-corrected results lowered the mean errors significantly and were comparable to what could be achieved with a much more expensive hybrid functional, but for reaction barrier heights and bond energies of molecules, the Hubbard correction was found to lower the mean error by only approximately a kcal/mol. As part of the analysis, we also compare VASP and Gaussian 09 calculations for the same density functional. [ABSTRACT FROM AUTHOR]

We present two new hybrid meta exchange- correlation functionals, called M06 and M06-2X. The M06 functional is parametrized including both transition metals and nonmetals, whereas the M06-2X functional is a high-nonlocality functional with double the amount of nonlocal exchange (2X), and it is parametrized only for nonmetals.The functionals, along with the previously published M06-L local functional and the M06-HF full-Hartree–Fock functionals, constitute the M06 suite of complementary functionals. We assess these four functionals by comparing their performance to that of 12 other functionals and Hartree–Fock theory for 403 energetic data in 29 diverse databases, including ten databases for thermochemistry, four databases for kinetics, eight databases for noncovalent interactions, three databases for transition metal bonding, one database for metal atom excitation energies, and three databases for molecular excitation energies. We also illustrate the performance of these 17 methods for three databases containing 40 bond lengths and for databases containing 38 vibrational frequencies and 15 vibrational zero point energies. We recommend the M06-2X functional for applications involving main-group thermochemistry, kinetics, noncovalent interactions, and electronic excitation energies to valence and Rydberg states. We recommend the M06 functional for application in organometallic and inorganometallic chemistry and for noncovalent interactions. [ABSTRACT FROM AUTHOR]

Hybrid density functional theory, which is a combined Hartree-Fock and density functional method, provides a simple but effective way to incorporate nonlocal exchange effects and static and dynamical correlation energy into an orbital-based theory with affordable computational cost for many important problems of gas-phase chemistry. The inclusion of a reaction field representing an implicit solvent in a self-consistent hybrid density functional calculation provides an effective and efficient way to extend this approach to problems of liquid-phase chemistry. In previous work, we have parameterized several models based on this approach, and in the present article, we present several new parameterizations based on implicit solvation models SM5.43 and SM5.43R. In particular, we extend the applicability of these solvation models to several combinations of the MPWXhybrid-density functional with various one-electron basis sets, where MPWXdenotes a combination of Barone and Adamo’s modified version of Perdew and Wang’s exchange functional, Perdew and Wang’s correlation functional, and a percentageXof exact Hartree-Fock exchange. SM5.43R parameter optimizations are presented for the MPWX/MIDI!, MPWX/MIDI!6D, and MPWX/6-31+G(d,p) combinations withX=0 (i.e., pure density functional theory), 25, 42.8, and 60.6, and for MPWX/6-31G(d) and MPWX/6-31+G(d), withX=0, 42.8, and 60.6; this constitutes a total of 18 new parameter sets. [Note that parameter optimizations using MPW25/6-31G(d) and MPW25/6-31+G(d) were carried out in a previous SM5.43R parameterization.] For each of the five basis sets, we found no significant loss in the accuracy of the model when parameters averaged over the four values ofXare used instead of the parameters optimized for a specific value ofX. Therefore for each of the five basis sets used here, the SM5.43R and SM5.43 models are defined to have a single parameter set that can be used for any value ofXbetween 0 and 60.6. The new models yield accurate free energies of solvation for a broad range of solutes in both water and organic solvents. On the average, the mean-unsigned errors, as compared with those from experiment, of the free energies of solvation of neutral solutes range from 0.50 to 0.55 kcal/mol and those for ions range from 4.5 to 4.9 kcal/mol. Since the SM5.43R model computes the free energy of solvation as a sum of bulk-electrostatic and non-bulk-electrostatic contributions, it may be used for detailed analysis of the physical effects underlying a calculation of the free energy of solvation. Several calculations illustrating the partitioning of these contributions for a variety of solutes inn-hexadecane, 1-octanol, and water are presented. [ABSTRACT FROM AUTHOR]

Equilibrium free-energy cycles relating oxidation and reduction potentials in solution to ionization potentials and electron affinities in the gas phase are constructed and the utilities of various levels of theory for computing particular free-energy changes within these cycles are discussed within the context of several examples. Emphasis is placed on the use of quantum-mechanical continuum solvation models to compute free energies of solvation. Key systems discussed include quinones, substituted anilines, substituted phenols, and reductive dechlorination reactions. [ABSTRACT FROM AUTHOR]

Beginning with the MIDI! basis set (also called MIDIX), we introduce the MIDIX+, MIDIY, and MIDIY+ basis sets. Using correlated ab initio and hybrid density functional theory, we compare their performance to that of several existing basis sets for electronic structure calculations. The new basis sets are tested with databases of 358 energies of reactions, 44 barrier heights, 31 electron affinities, 18 geometries, and 29 dipole moments. The MIDI!, MIDIX+, MIDIY, and MIDIY+ basis sets are shown to be cost-efficient methods for calculating relative energies, geometries, and dipole moments. The MIDIX+ basis is shown to be particularly efficient for calculating electron affinities of large molecules. [ABSTRACT FROM AUTHOR]

A highly selective Ir catalyst supported on the metal–organic framework (MOF) UiO-67 for the catalytic borylation of methane has recently been synthesized. The high chemoselectivity of the catalyst toward monoborylated methane (CH3Bpin, Bpin = pinacolborane) instead of diborylated methane (CH2Bpin2) was speculated to be caused by the steric confinement of MOF UiO-67. In this study, we applied quantum mechanical methods to determine: (1) the steric effect of the UiO-67 framework in promoting the chemoselectivity of the Ir catalyst toward CH3Bpin and (2) the borylation mechanisms over the Ir catalyst supported on UiO-67. Our results show that UiO-67 framework sterically obstructs the diffusion of the larger CH2Bpin2 molecule within the MOF while allowing the smaller CH3Bpin molecule to pass through with little energy penalty. The diffusion of CH2Bpin2 from the tetrahedral pore to the tetragonal pyramidal pore within modified UiO-67 with coordinated Ir(Bpin)3 complex has an estimated barrier of 24.7 kcal/mol and is 14.2 kcal/mol higher than the diffusion of CH3Bpin. The electronic and steric effects of the support at the Ir catalytic center are much smaller than this confinement effect on diffusion, and the catalytic center behaves similarly to the homogeneous Ir catalyst. We determined an overall free energy of activation of 34.6 kcal/mol for the CH4 borylation reaction using the Ir(III) catalyst. We also determined that the turnover-determining step for the catalytic methane borylation is the isomerization of seven-coordinated Ir(V) complex instead of the commonly assumed C–H bond activation by oxidative addition. [ABSTRACT FROM AUTHOR]

The article presents information on the journal "Theoretical Chemistry Accounts: Theory, Computation, & Modeling" (TCA). The journal is opening a new editorial office in China, where chemistry professor Yundong Wu will be associate editor. It is reported that TCA is the oldest journal in the world dedicated to the topic of theoretical chemistry, and it has a long and distinguished history of publishing some of the most important papers in the field.

A correction to the article "The M06 Suite of Density Functionals for Main Group Thermochemistry, Thermochemical Kinetics, Noncovalent Interactions, Excited States, and Transition Elements: Two New Functionals and Systematic Testing of Four M06 Functionals and 12 Other Functionals," that was published in a previous issue is presented.

The article reflects on the developments of the 2006 issue of the periodical "Theoretical Chemistry Accounts." The recent issue presented 33 articles which cover areas related to theoretical chemistry by modern theoretical chemists. Senior advisers suggested contributors including Biman Bagchi, Vincenzo Barone, Charles Brooks and other colleagues.