: 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

The conductor-like solvation model, as developed in the framework of the polarizable continuum model (PCM), has been reformulated and newly implemented in order to compute energies, geometric structures, harmonic frequencies, and electronic properties in solution for any chemical system that can be studied in vacuo Particular attention is devoted to large systems requiring suitable iterative algorithms to compute the solvation charges: the fast multipole method (FMM) has been extensively used to ensure a linear scaling of the computational times with the size of the solute A number of test applications are presented to evaluate the performances of the method

Energies, structures, and electronic properties of molecules in solution with the C-PCM solvation model.

COSMO-RS, a general and fast methodology for the a priori prediction of thermophysical data of liquids is presented. It is based on cheap unimolecular quantum chemical calculations, which, combined with exact statistical thermodynamics, provide the information necessary for the evaluation of molecular interactions in liquids. COSMO-RS is an alternative to structure interpolating group contribution methods. The method is independent of experimental data and generally applicable. A methodological comparison with group contribution methods is given. The applicability of the COSMO-RS method to the goal of solvent screening is demonstrated at various examples of vapor–liquid-, liquid–liquid-, solid–liquid-equilibria and vapor-pressure predictions.

Fast solvent screening via quantum chemistry: COSMO‐RS approach

TURBOMOLE is a collaborative, multi-national software development project aiming to provide highly efficient and stable computational tools for quantum chemical simulations of molecules, clusters, periodic systems, and solutions. The TURBOMOLE software suite is optimized for widely available, inexpensive, and resource-efficient hardware such as multi-core workstations and small computer clusters. TURBOMOLE specializes in electronic structure methods with outstanding accuracy-cost ratio, such as density functional theory including local hybrids and the random phase approximation (RPA), GW-Bethe-Salpeter methods, second-order Moller-Plesset theory, and explicitly correlated coupled-cluster methods. TURBOMOLE is based on Gaussian basis sets and has been pivotal for the development of many fast and low-scaling algorithms in the past three decades, such as integral-direct methods, fast multipole methods, the resolution-of-the-identity approximation, imaginary frequency integration, Laplace transform, and pair natural orbital methods. This review focuses on recent additions to TURBOMOLE's functionality, including excited-state methods, RPA and Green's function methods, relativistic approaches, high-order molecular properties, solvation effects, and periodic systems. A variety of illustrative applications along with accuracy and timing data are discussed. Moreover, available interfaces to users as well as other software are summarized. TURBOMOLE's current licensing, distribution, and support model are discussed, and an overview of TURBOMOLE's development workflow is provided. Challenges such as communication and outreach, software infrastructure, and funding are highlighted.

/pdf/turbomole-modular-program-suite-for-ab-initio-quantum-4pumrnnyz6.pdf

TURBOMOLE: Modular program suite for ab initio quantum-chemical and condensed-matter simulations

An activity coefficient model using molecular solvation based on the COSMO-RS method is proposed. In this model, quantum mechanical COSMO calculations are performed to obtain the screening charges for molecules in a perfect conductor. A statistical mechanical model that considers molecules to be a collection of surface segments is developed for the calculation of segment activity coefficients using these screening charges. Activity coefficients for molecules are then obtained by summing the contributions of the segments. This model requires only a single radius for each atom in the COSMO solvation calculations, one universal parameter to discern hydrogen-bond acceptors and donors, and two universal parameters to determine segment interactions. This is a significantly fewer number of parameters for phase equilibrium calculations than group contribution methods such as the UNIFAC (168 parameters) and modified UNIFAC (612 parameters) models. The resulting completely a priori prediction method results in abso...

A Priori Phase Equilibrium Prediction from a Segment Contribution Solvation Model

The most recent algorithmic enhancements of the COSMO solvation model are presented and the implementation in the TURBOMOLE program package is described. Three demonstrative applications covering homogeneous catalysis, tautomeric equilibria, and binary phase diagrams show the efficiency and general applicability of the approach. Especially when combined with the COSMO-RS extension, the method very reliably predicts thermodynamic properties of liquid mixtures.

COSMO Implementation in TURBOMOLE: Extension of an efficient quantum chemical code towards liquid systems

The vapor pressures and vaporization enthalpies of a series of 1-n-alkyl-3-methylimidazolium-bis-(trifluoromethanesulfonyl) amide ionic liquids have been predicted with two different approaches using the COSMO-RS method and quantum chemical gas phase calculations. While the calculated enthalpies are in good agreement with the experimental data, COSMO-RS seems to underestimate the vapor pressures by roughly 0.5–4 log units dependent on the IL and approach used.

Prediction of the vapor pressure and vaporization enthalpy of 1-n-alkyl-3-methylimidazolium-bis-(trifluoromethanesulfonyl) amide ionic liquids

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COSMO Implementation in TURBOMOLE: Extension of an efficient quantum chemical code towards liquid systems

Prediction of the vapor pressure and vaporization enthalpy of 1-n-alkyl-3-methylimidazolium-bis-(trifluoromethanesulfonyl) amide ionic liquids