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.

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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-class functionals and 12 other functionals

6.2.2. Definition of Effective Properties 3064 6.3. Response Properties to Magnetic Fields 3066 6.3.1. Nuclear Shielding 3066 6.3.2. Indirect Spin−Spin Coupling 3067 6.3.3. EPR Parameters 3068 6.4. Properties of Chiral Systems 3069 6.4.1. Electronic Circular Dichroism (ECD) 3069 6.4.2. Optical Rotation (OR) 3069 6.4.3. VCD and VROA 3070 7. Continuum and Discrete Models 3071 7.1. Continuum Methods within MD and MC Simulations 3072

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Quantum mechanical continuum solvation models.

We present the theoretical and technical foundations of the Amsterdam Density Functional (ADF) program with a survey of the characteristics of the code (numerical integration, density fitting for the Coulomb potential, and STO basis functions). Recent developments enhance the efficiency of ADF (e.g., parallelization, near order-N scaling, QM/MM) and its functionality (e.g., NMR chemical shifts, COSMO solvent effects, ZORA relativistic method, excitation energies, frequency-dependent (hyper)polarizabilities, atomic VDD charges). In the Applications section we discuss the physical model of the electronic structure and the chemical bond, i.e., the Kohn–Sham molecular orbital (MO) theory, and illustrate the power of the Kohn–Sham MO model in conjunction with the ADF-typical fragment approach to quantitatively understand and predict chemical phenomena. We review the “Activation-strain TS interaction” (ATS) model of chemical reactivity as a conceptual framework for understanding how activation barriers of various types of (competing) reaction mechanisms arise and how they may be controlled, for example, in organic chemistry or homogeneous catalysis. Finally, we include a brief discussion of exemplary applications in the field of biochemistry (structure and bonding of DNA) and of time-dependent density functional theory (TDDFT) to indicate how this development further reinforces the ADF tools for the analysis of chemical phenomena. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 931–967, 2001

Chemistry with ADF

There are now a wide variety of packages for electronic structure calculations, each of which differs in the algorithms implemented and the output format. Many computational chemistry algorithms are only available to users of a particular package despite being generally applicable to the results of calculations by any package. Here we present cclib, a platform for the development of package-independent computational chemistry algorithms. Files from several versions of multiple electronic structure packages are automatically detected, parsed, and the extracted information converted to a standard internal representation. A number of population analysis algorithms have been implemented as a proof of principle. In addition, cclib is currently used as an input filter for two GUI applications that analyze output files: PyMOlyze and GaussSum. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008

cclib: A library for package‐independent computational chemistry algorithms

We present a new local density functional, called M06-L, for main-group and transition element thermochemistry, thermochemical kinetics, and noncovalent interactions. The functional is designed to capture the main dependence of the exchange-correlation energy on local spin density, spin density gradient, and spin kinetic energy density, and it is parametrized to satisfy the uniform-electron-gas limit and to have good performance for both main-group chemistry and transition metal chemistry. The M06-L functional and 14 other functionals have been comparatively assessed against 22 energetic databases. Among the tested functionals, which include the popular B3LYP, BLYP, and BP86 functionals as well as our previous M05 functional, the M06-L functional gives the best overall performance for a combination of main-group thermochemistry, thermochemical kinetics, and organometallic, inorganometallic, biological, and noncovalent interactions. It also does very well for predicting geometries and vibrational frequencies. Because of the computational advantages of local functionals, the present functional should be very useful for many applications in chemistry, especially for simulations on moderate-sized and large systems and when long time scales must be addressed. © 2006 American Institute of Physics. DOI: 10.1063/1.2370993

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A new local density functional for main-group thermochemistry, transition metal bonding, thermochemical kinetics, and noncovalent interactions.

In this Tutorial Review, we make the point that a true understanding of trends in reactivity (as opposed to measuring or simply computing them) requires a causal reactivity model. To this end, we present and discuss the Activation Strain Model (ASM). The ASM establishes the desired causal relationship between reaction barriers, on one hand, and the properties of reactants and characteristics of reaction mechanisms, on the other hand. In the ASM, the potential energy surface ΔE(ζ) along the reaction coordinate ζ is decomposed into the strain ΔEstrain(ζ) of the reactants that become increasingly deformed as the reaction proceeds, plus the interaction ΔEint(ζ) between these deformed reactants, i.e., ΔE(ζ) = ΔEstrain(ζ) + ΔEint(ζ). The ASM can be used in conjunction with any quantum chemical program. An analysis of the method and its application to problems in organic and organometallic chemistry illustrate the power of the ASM as a unifying concept and a tool for rational design of reactants and catalysts.

The activation strain model and molecular orbital theory: understanding and designing chemical reactions.

Up till now, there has been a significant disagreement between theory and experiment regarding hydrogen bond lengths in Watson−Crick base pairs. To investigate the possible sources of this discrepancy, we have studied numerous model systems for adenine−thymine (AT) and guanine−cytosine (GC) base pairs at various levels (i.e., BP86, PW91, and BLYP) of nonlocal density functional theory (DFT) in combination with different Slater-type orbital (STO) basis sets. Best agreement with available gas-phase experimental A−T and G−C bond enthalpies (−12.1 and −21.0 kcal/mol) is obtained at the BP86/TZ2P level, which (for 298 K) yields −11.8 and −23.8 kcal/mol. However, the computed hydrogen bond lengths show again the notorious discrepancy with experimental values. The origin of this discrepancy is not the use of the plain nucleic bases as models for nucleotides:  the disagreement with experiment remains no matter if we use hydrogen, methyl, deoxyribose, or 5‘-deoxyribose monophosphate as the substituents at N9 and N...

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Hydrogen Bonding in DNA Base Pairs: Reconciliation of Theory and Experiment

The view that the hydrogen bonds in Watson - Crick adenine - thy- mine (AT) and guanine - cytosine (GC) base pairs are in essence electrostatic interactions with substantial resonance assistance from the p electrons is ques- tioned. Our investigation is based on a state-of-the-art density functional theo- retical (DFT) approach (BP86/TZ2P) that has been shown to properly repro- duce experimental data. Through a quantitative decomposition of the hy- drogen bond energy into its various physical terms, we demonstrate that, contrary to the widespread belief, do- nor - acceptor orbital interactions (i.e., charge transfer) in s symmetry between N or O lone pairs on one base and NH s*-acceptor orbitals on the other base do provide a substantial bonding contri- bution which is, in fact, of the same order of magnitude as the electrostatic interaction term. The overall orbital interactions are reinforced by a small p component which stems from polariza- tion in the p-electron system of the individual bases. This p component is, however, one order of magnitude small- er than the s term. Furthermore, we have investigated the synergism in a base pair between charge transfer from one base to the other through one hydrogen bond and in the opposite direction through another hydrogen bond, as well as the cooperative effect between the donor - acceptor interac- tions in the s- and polarization in the p- electron system. The possibility of CH ··· O hydrogen bonding in AT is also examined. In the course of these analyses, we introduce an extension of the Voronoi deformation density (VDD) method which monitors the redistribution of the s- and p-electron densities individually out of (DQ> 0) or into (DQ< 0) the Voronoi cell of an atom upon formation of the base pair from the separate bases.

The Nature of the Hydrogen Bond in DNA Base Pairs: The Role of Charge Transfer and Resonance Assistance

The strength of the CN/CN' bond decreases in the series NC-CN (1), CN-CN (2), and CN-NC (3), while simultaneously it shortens. The explanation requires that, apart from the σ pair bond between the CN 5σ MO's, the following effects be taken into account: (a) Pauli repulsion («steric hindrance») between the 4σ («N lone pair») orbitals; (b) Pauli repulsion between the 4σ and 5σ orbitals; (c) donor/acceptor interaction between the 4σ and 5σ orbitals; (d) donor/acceptor interaction between the occupied 1 π and unoccupied 2π *

F.M. Bickelhaupt

Papers

Chemistry with ADF

The activation strain model and molecular orbital theory: understanding and designing chemical reactions.

Hydrogen Bonding in DNA Base Pairs: Reconciliation of Theory and Experiment

The Nature of the Hydrogen Bond in DNA Base Pairs: The Role of Charge Transfer and Resonance Assistance

Central Bond in the Three CN• Dimers NC–CN, CN–CN and CN–NC: Electron Pair Bonding and Pauli Repulsion Effects