Systematic study of vibrational frequencies calculated with the self‐consistent charge density functional tight‐binding method

Abstract

We present a detailed study of harmonic vibrational frequencies obtained with the self-consistent charge density functional tight-binding (SCC-DFTB) method. Our testing set comprises 66 molecules and 1304 distinct vibrational modes. Harmonic vibrational frequencies are computed using an efficient analytical algorithm developed and coded by the authors. The obtained results are compared to experiment and to other theoretical findings. Scaling factor for the SCC-DFTB method, determined by minimization of mean absolute deviation of scaled frequencies, is found to be 0.9933. The accuracy of the scaled SCC-DFTB frequencies is noticeably better than for other semiempirical methods (including standard DFTB method) and approximately twice worse than for other well established scaled ab initio quantum chemistry methods (e.g., HF, BLYP, B3LYP). Mean absolute deviation for the scaled SCC-DFTB frequencies is 56 cm(-1), while standard deviation is 82 cm(-1), and maximal absolute deviation is as large as 529 cm(-1). Using SCC-DFTB allows for substantial time savings; computational time is reduced from hours to seconds when compared to standard ab initio techniques.

Mechanism of Back Electron Transfer in an Intermolecular Photoinduced Electron Transfer Reaction: Solvent as a Charge Mediator

“…Unfortunately, the dimer cation Py 2 C + proved to be too complex a system for DFT, which could not describe realistically either of the features responsible for bonding in Py 2 C + , that is, dispersion forces that glue the monomers together and the multireference character of its wave function responsible for the charge delocalization between both monomers. [13] The calculated band at 1201 cm À1 appears to be missing in the experimental spectrum, and this could be because we have simulated the monomer spectrum and not the dimer spectrum. The FTIR spectrum of Py in ACN ( Figure 2a) shows three prominent bands at 1244, 1186, and 1096 cm À1 , which are well reproduced in the calculated IR spectrum ( Figure 2b) at 1235, 1182, and 1088 cm À1 , respectively.…”

The vibrational spectra of protonated water clusters: A benchmark for self-consistent-charge density-functional tight binding

“…The computational efficiency of SCC-DFTB makes it, in principle, an attractive choice in this context and complementary to calculations based on much more expensive QM methods that might suffer from convergence issues. 10 Although previous studies based on NMA indicate that SCC-DFTB overall gives favorable vibrational frequencies among semiempirical methods, 28,29 whether it is capable of capturing the spectroscopic signatures of various water clusters remains unknown. In this study, we carry out SCC-DFTB calculations for the IR spectra of various protonated water clusters in the gas phase and compare the results to experimental spectra, which only became available very recently.…”

Molecular dynamics and density functional theory studies of substrate binding and catalysis of human brain aspartoacylase

“…The SCC-DFTB method has been extensively tested [19][20][21][22] and applied successfully to several important enzymatic systems [23][24][25][26]. Here the QM/MM molecular dynamics (MD) studies the Michaelis complex of hASPA with its substrate NAA, which shed light on the active-site arrangement.…”