Modeling vibrational spectra using the self-consistent charge density-functional tight-binding method. I. Raman spectra

Abstract

Articles you may be interested in Universal tight binding model for chemical reactions in solution and at surfaces. III. Stoichiometric and reduced surfaces of titania and the adsorption of water As is now well established, a first order expansion of the Hohenberg-Kohn total energy density functional about a trial input density, namely, the Harris-Foulkes functional, can be used to rationalize a non self consistent tight binding model. If the expansion is taken to second order then the energy and electron density matrix need to be calculated self consistently and from this functional one can derive a charge self consistent tight binding theory. In this paper we have used this to describe a polarizable ion tight binding model which has the benefit of treating charge transfer in point multipoles. This admits a ready description of ionic polarizability and crystal field splitting. It is necessary in constructing such a model to find a number of parameters that mimic their more exact counterparts in the density functional theory. We describe in detail how this is done using a combination of intuition, exact analytical fitting, and a genetic optimization algorithm. Having obtained model parameters we show that this constitutes a transferable scheme that can be applied rather universally to small and medium sized organic molecules. We have shown that the model gives a good account of static structural and dynamic vibrational properties of a library of molecules, and finally we demonstrate the model's capability by showing a real time simulation of an enolization reaction in aqueous solution. In two subsequent papers, we show that the model is a great deal more general in that it will describe solvents and solid substrates and that therefore we have created a self consistent quantum mechanical scheme that may be applied to simulations in heterogeneous catalysis. © 2014 AIP Publishing LLC.

Comparison of geometric, electronic, and vibrational properties for all pentagon/hexagon‐bearing isomers of fullerenes C38, C40, and C42

“…For calculating frequencies, we have used analytical Hessian recently implemented in the original code 14. Intensities in vibrational spectra have been computed using numerical derivatives of gradient with respect to the components of external electric field 15, 16. The theoretical Raman spectra have been generated 16 assuming that the experimental spectra were recorded at 25°C and with the excitation laser frequency of 9398.5 cm −1 .…”

“…Intensities in vibrational spectra have been computed using numerical derivatives of gradient with respect to the components of external electric field 15, 16. The theoretical Raman spectra have been generated 16 assuming that the experimental spectra were recorded at 25°C and with the excitation laser frequency of 9398.5 cm −1 . Initial geometries of the fullerene isomers were taken from the “Fullerene Structure Library” 17.…”

Implementation and benchmark tests of the DFTB method and its application in the ONIOM method

“…With a careful parameterization, errors in semiempirical calculations are often within a qualitatively acceptable range. Consequently, efforts in the development and applications of semiempirical methods still continue more than three decades after their inception 2–29. Semiempirical methods are also considered to be the low‐level QM method in hybrid ONIOM (QM:QM′) or ONIOM (QM:QM′:MM) methods 30–34.…”

Dcdftbmd: Divide‐and‐Conquer Density Functional Tight‐Binding Program for Huge‐System Quantum Mechanical Molecular Dynamics Simulations

“…D cdftbmd can apply point charges and static electric field for the SCC‐based models to include external field effects. The former correction to the total energy is written as where Q a is the external charge.…”

“…For l ‐shell resolved and open‐shell calculations, numerical harmonic frequencies obtained from differentiation of analytical gradients are currently supported. The infrared intensities and Raman activities are calculated at the DFTB2 and DFTB3 levels following the procedure by Witek and coworkers . The thermodynamic quantities are evaluated in the standard manner.…”