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 openshell 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 Cr 2 dimer, exploring zeolitecatalysed 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.Keywords quantum chemistry, software, electronic structure theory, density functional theory, electron correlation, computational modelling, Q-Chem Disciplines Chemistry CommentsThis article is from Molecular Physics: An International Journal at the Interface Between Chemistry and Physics 113 (2015): 184, doi:10.1080/00268976.2014. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. Authors 185A 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 corre...

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange–correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear–electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an “open teamware” model and an increasingly modular design.

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<p>To facilitate computational investigation of intermolecular interactions in the solution phase, we report the development of ALMO-EDA(solv), a scheme that allows the application of continuum solvent models within the framework of energy decomposition analysis (EDA) based on absolutely localized molecular orbitals (ALMOs). In this scheme, all the quantum mechanical states involved in the variational EDA procedure are computed with the presence of solvent environment so that solvation effects are incorporated in the evaluation of all its energy components. After validation on several model complexes, we employ ALMO-EDA(solv) to investigate substituent effects on two classes of complexes that are related to electrochemical CO₂ reduction catalysis. For [FeTPP(CO₂−κC)]²⁻ (TPP = tetraphenylporphyrin), we reveal that two ortho substituents which yield most favorable CO2 binding, −N(CH₃)₃⁺ (TMA) and −OH, stabilize the complex via through-structure and through-space mechanisms, respectively. The Coulombic interaction between the positively charged TMA group and activated CO₂ is found to be largely attenuated by the polar solvent. Furthermore, we also provide computational support for the design strategy of utilizing bulky, flexible ligands to stabilize activated CO₂ via long-range Coulomb interactions, which creates biomimetic solvent-inaccessible “pockets” in that electrostatics is unscreened. For the reactant and product complexes associated with the electron transfer from the <i>p</i>-terphenyl radical anion to CO₂ , we demonstrate that the double terminal substitution of <i>p</i>-terphenyl by electron-withdrawing groups considerably strengthens the binding in the product state while moderately weakens that in the reactant state, which are both dominated by the substituent tuning of the electrostatics component. These applications illustrate that this new extension of ALMO-EDA provides a valuable means to unravel the nature of intermolecular interactions and quantify their impacts on chemical reactivity in solution.<br></p>

This work examines the viability of matrix completion methods as cost-effective alternatives to full nuclear Hessians for calculating quantum and variational effects in chemical reactions. The harmonic variety-based matrix completion (HVMC) algorithm, developed in a previous study (https://doi.org/10.1063/5.0018326), exploits the low-rank character of the polynomial expansion of potential energy to recover, using a small sample, vibrational frequencies (square roots of nuclear Hessian eigenvalues) constituting the reaction path. These frequencies are essential for calculating rate coefficients using variational transition state theory with multidimensional tunneling (VTST-MT). HVMC performance is examined for four SN2 reactions and five hydrogen transfer reactions, with each H-transfer reaction consisting of at least one vibrational mode strongly coupled to the reaction coordinate. HVMC is robust and captures zero-point energies, vibrational free energies, zero-curvature tunneling, and adiabatic ground state and free energy barriers as well as their positions on the reaction coordinate. For medium to large reactions involving H- transfer, with the exception of the most complex Ir catalysis system, less than 35% of total eigenvalue information is necessary for accurate recovery of key VTST-MT observables.

Reactions of poly(vinyl chloride) (PVC) with a rhodium catalyst and H-donors reveal how reaction conditions can impact the selectivity for chloride removal, with sodium formate showing the highest selectivity for hydrodechlorination.

<div> <div> <div> <p>We present a fundamental description of the electron transfer (ET) step from substituted oligo(p-phenylene) (OPP) radical anions to CO2, with the larger goal of assessing the viability of underexplored, organic photoredox routes for utilization of anthropogenic CO2. This work varies the electrophilicity of para-substituents to OPP and probes the dependence of rate coefficients and interfragment interactions on the substituent Hammett parameter, σp, using constrained density functional theory (CDFT) and energy decomposition analysis (EDA). Large electronic coupling elements across substituents indicate an adiabatic electron transfer process for reactants at contact. As one might intuitively expect, free energy changes dominate trends in ET rate coefficients in most cases, and rates increase with substituent electron-donating ability. However, we observe an unexpected dip in rate coefficients for the most electron- donating groups, due to the combined impact of flattening free energies and a steep increase in reorganization energies. Our analysis shows that flattening OPP LUMO levels lower the marginal increase in free energy with decreasing σp. Reorganization energies do not exhibit a direct dependence on σp. They are higher for substituents containing lone pairs of electrons since substituent orientation varies with OPP charge. EDA reveals that interfragment orbital relaxation, or charge transfer interaction, plays a critical role in stabilizing the vertically excited charge transfer state. Subsequent relaxation to the final state geometry lowers charge transfer stabilization. A concurrent increase in long-range electrostatic interactions is observed, which are more favorable for electron-withdrawing substituents. Our study therefore suggests that while a wide range of ET rates are observed, there is an upper limit to rate enhancements achievable by tuning substituent electrophilicity.</p></div></div></div>

In present we have been producing metallic nanoparticles with toxic and harmful chemicals which are more dangerous to environment. Therefore there is a need to develop environment friendly synthesis techniques without using toxic chemicals. In this work a simple and green/eco-friendly/chemical free biosynthesis of silver nanoparticles using C seed extract as reducing agents was prepared. Nanoparticles were characterized by UV-vis absorbance spectroscopy, XRD and SEM measurements. The metal ions reduction occurs very rapidly, and the reduction of Ag ions will be completed within 4 hours. The synthesized silver Nanoparticle distinct monodispersity as they show particle size between the ranges of 30-80 nm. The experimental study confirmed the formation of highly crystalline nanoparticles with uniform shape. Further, the antibacterial activity against the Bacillus subtilis was also evaluated for Elettaria cardamom seeds extract assisted silver nanoparticles and the later found to exhibit significant activity.