Calculations Of IR Spectra Research Articles

Vibrational absorption spectra from vibrational coupled cluster damped linear response functions calculated using an asymmetric Lanczos algorithm

We report the theory and implementation of vibrational coupled cluster (VCC) damped response functions. From the imaginary part of the damped VCC response function the absorption as function of frequency can be obtained, requiring formally the solution of the now complex VCC response equations. The absorption spectrum can in this formulation be seen as a matrix function of the characteristic VCC Jacobian response matrix. The asymmetric matrix version of the Lanczos method is used to generate a tridiagonal representation of the VCC response Jacobian. Solving the complex response equations in the relevant Lanczos space provides a method for calculating the VCC damped response functions and thereby subsequently the absorption spectra. The convergence behaviour of the algorithm is discussed theoretically and tested for different levels of completeness of the VCC expansion. Comparison is made with results from the recently reported [P. Seidler, M. B. Hansen, W. Györffy, D. Toffoli, and O. Christiansen, J. Chem. Phys. 132, 164105 (2010)] vibrational configuration interaction damped response function calculated using a symmetric Lanczos algorithm. Calculations of IR spectra of oxazole, cyclopropene, and uracil illustrate the usefulness of the new VCC based method.

Ab initio potential and dipole moment surfaces for water. II. Local-monomer calculations of the infrared spectra of water clusters

We employ recent flexible ab initio potential energy and dipole surfaces [Y. Wang, X. Huang, B. C. Shepler, B. J. Braams, and J. M. Bowman, J. Chem. Phys. 134, 094509 (2011)] to the calculation of IR spectra of the intramolecular modes of water clusters. We use a quantum approach that begins with a partitioned normal-mode analysis of perturbed monomers, and then obtains solutions of the corresponding Schrödinger equations for the fully coupled intramolecular modes of each perturbed monomer. For water clusters, these modes are the two stretches and the bend. This approach is tested against benchmark calculations for the water dimer and trimer and then applied to the water clusters (H(2)O)(n) for n = 6-10 and n = 20. Comparisons of the spectra are made with previous ab initio harmonic and empirical potential calculations and available experiments.

Nonempirical calculation of structural, electric and spectral characteristics of diprazine

Calculations of IR spectra, dipole moments, atomic charges, and structural characteristics of three forms of diprazine (molecular, cation and dication) were carried out. Changes in the studied characteristics in going from one form to another were analyzed.

The quantum in chemistry: an experimentalist's view

The quantum in chemistry: an experimentalist's view

Calculations of IR-spectra of metastable bond isomers of ruthenium nitrosocomplexes [Ru(NO)Cl5]2− [Ru(NO)(CN)5]2− by DFT method

IR-spectra of stable and metastable isomers of ruthenium nitrosocomplexes, [Ru(NO)Cl5]2− and [Ru(NO)(CN)5]2−, have been calculated within the frames of density functional theory. Frequency assignment was refined on the base of analysis of normal vibration in internal vibrational coordinates. Calculation results confirm that spectrally observed metastable states are bond isomers with ν1-ON and ν2-NO coordination.

Engineering calculations of optical spectra of large molecules and polymers

The sense of the term “engineering” is discussed with respect to calculating the optical spectra of complex compounds (large molecules, polymers and molecular crystals). The conditions which have to be satisfied when choosing the most expedient strategies for developing methods of the engineering calculations at the molecular level are introduced. The relationship between the ab initio and semiempirical methods is analyzed. The features of solving inverse spectral problems, the occurrence of subjective factors in the course of the solution, and the effect of the factors on the compilation of the respective knowledge banks are discussed. The engineering calculations of IR spectra are exemplified. The ways of developing the methods for the engineering calculations of selected spectra of complex compounds are analyzed. The potential of the current theory is illustrated.

Engineering calculations of IR spectra of complex molecules

General principles for accumulating molecular parameters with a view to performing bulk (engineering) calculations of IR spectra of complex organic and hetero-organic compounds are presented and the search for the parameters, by carrying out consistent quantum-chemical calculations and by solving inverse spectral problems, is described. The potentials of the calculations of IR spectra using the available data banks are demonstrated.