Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package, together with illustrative timings and applications. Specific developments discussed include fast methods for density functional theory calculations, linear scaling evaluation of energies, NMR chemical shifts and electric properties, fast auxiliary basis function methods for correlated energies and gradients, equation-of-motion coupled cluster methods for ground and excited states, geminal wavefunctions, embedding methods and techniques for exploring potential energy surfaces.

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Advances in methods and algorithms in a modern quantum chemistry program package

A summary of the technical advances that are incorporated in the fourth major release of the Q-Chem quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and open-shell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order Moller–Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly correlated Cr_2 dimer, exploring zeolite-catalysed ethane dehydrogenation, energy decomposition analysis of a charged ter-molecular complex arising from glycerol photoionisation, and natural transition orbitals for a Frenkel exciton state in a nine-unit model of a self-assembling nanotube.

/pdf/advances-in-molecular-quantum-chemistry-contained-in-the-q-3j7dwbtpjv.pdf

Advances in molecular quantum chemistry contained in the Q-Chem 4 program package

A summary of the technical advances that are incorporated in the fourth major release of the Q-Chem quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and open-shell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order Møller–Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly correlated Cr2 dimer, exploring zeolite-catalysed ethane dehydrogenation, energy decomposition analysis of a charged ter-molecular complex arising from glycerol photoionisation, and natural transition orbitals for a Frenkel exciton state in a nine-unit model of a self-assembling nanotube.

RESEARCH ARTICLE Advances in molecular quantum chemistry contained in the Q-Chem 4 program package

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

This review describes a multidimensional treatment of molecular recognition phenomena involving aromatic rings in chemical and biological systems. It summarizes new results reported since the appearance of an earlier review in 2003 in host-guest chemistry, biological affinity assays and biostructural analysis, data base mining in the Cambridge Structural Database (CSD) and the Protein Data Bank (PDB), and advanced computational studies. Topics addressed are arene-arene, perfluoroarene-arene, S⋅⋅⋅aromatic, cation-π, and anion-π interactions, as well as hydrogen bonding to π systems. The generated knowledge benefits, in particular, structure-based hit-to-lead development and lead optimization both in the pharmaceutical and in the crop protection industry. It equally facilitates the development of new advanced materials and supramolecular systems, and should inspire further utilization of interactions with aromatic rings to control the stereochemical outcome of synthetic transformations.

Aromatic rings in chemical and biological recognition: energetics and structures.

Ab initio NMR spectra for molecular systems with a thousand and more atoms: a linear-scaling method.

Structure and Dynamics of the Host–Guest Complex of a Molecular Tweezer: Coupling Synthesis, Solid-State NMR, and Quantum-Chemical Calculations

A Study of a Molecular Tweezer Host–Guest System by a Combination of Quantum-Chemical Calculations and Solid-State NMR Experiments☆

A new class of receptor molecules is presented that is highly selective for N-alkylpyridinium ions and electron-poor aromatics. Its key feature is the combination of a well-preorganized molecular clip with an electron-rich inner cavity and strategically placed, flanking bis-phosphonate monoester anions. This shape and arrangement of binding sites attracts predominantly flat electron-poor aromatics in water, binds them mainly by pi-cation, pi-pi, CH-pi, and hydrophobic interactions, and leads to their highly efficient desolvation. NAD(+) and NADP, the important cofactors of many redox enzymes, are recognized by the new receptor molecule, which embraces the catalytically active nicotinamide site and the adenine unit. Even nucleosides such as adenosine are likewise drawn into the clip's cavity. Complex formation and structures were examined by one- and two-dimensional NMR spectroscopy, Job plot analyses, and isothermal titration microcalorimetric (ITC) measurements, as well as quantum chemical calculations of (1)H NMR shifts. The new receptor molecule is a promising tool for controlling enzymatic oxidation processes and for DNA chemistry.

Selective Complexation of N‐Alkylpyridinium Salts: Binding of NAD+ in Water

The structure of supramolecular complexes formed by a naphthalene-spaced tweezer molecule as host and 1,4-dicyanobenzene (DCNB), 1,2,4,5-tetracyanobenzene (TCNB), and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) as aromatic, electron-deficient guests is investigated by solid-state NMR and X-ray diffraction measurements. Quantum chemical calculations using linear scaling methods are applied to predict and to assign the 1H NMR chemical shifts of the complexes. By combining experiment and theory, insights into intra- and intermolecular effects influencing the proton chemical shifts of the host−guest system are provided in the solid state.

Felix Koziol

Papers

Ab initio NMR spectra for molecular systems with a thousand and more atoms: a linear-scaling method.

Structure and Dynamics of the Host–Guest Complex of a Molecular Tweezer: Coupling Synthesis, Solid-State NMR, and Quantum-Chemical Calculations

A Study of a Molecular Tweezer Host–Guest System by a Combination of Quantum-Chemical Calculations and Solid-State NMR Experiments☆

Selective Complexation of N‐Alkylpyridinium Salts: Binding of NAD+ in Water

Structure of molecular tweezer complexes in the solid state: NMR experiments, X-ray investigations, and quantum chemical calculations.