An Improved Self-Consistent-Charge Density-Functional Tight-Binding (SCC-DFTB) Set of Parameters for Simulation of Bulk and Molecular Systems Involving Titanium

Abstract

A new self-consistent-charge density-functional tight-binding (SCC-DFTB) set of parameters for Ti-X pairs of elements (X = Ti, H, C, N, O, S) has been developed. The performance of this set has been tested with respect to TiO2 bulk phases and small molecular systems. It has been found that the band structures, geometric parameters, and cohesive energies of rutile and anatase polymorphs are in good agreement with the reference DFT data and with experiment. Low-index rutile and anatase surfaces were also tested. For molecular systems, binding and atomization energies close to their DFT analogues have been achieved. Large errors, however, have been found for systems in high-spin states and/or having multireference character of their wave functions. The correct performance of SCC-DFTB for surface reactions has been demonstrated via the water splitting on anatase (001) surface. The current SCC-DFTB set is a suitable tool for future in-depth investigation of chemical processes occurring on the surfaces of TiO2 polymorphs as well as for other processes of physicochemical interest.

Acene‐Modified Triphenylamine Dyes for Dye‐Sensitized Solar Cells: A Computational Study

“…For the organic dye/(TiO 2 ) 46 system with more than 200 atoms, we took advantage of the efficiency of the DFTB method for the geometry optimizations, and DFT/TDDFT methods for the electronic structure and vertical excitation energies analysis. The DFTB model was derived from a second-order expansion of the DFT total energy functional with respect to charge density fluctuations; at the same time, the Hamiltonian matrix elements are calculated with a two-center approximation.…”

“…[44][45][46] The full geometric optimizations were performed using the conjugate gradient algorithm until the residual forces were below 5 10 À4 au; we also set the charge convergence criterion to 10 À5 electrons. The DFTB-optimized dye/(TiO 2 ) 46 nanoparticles were followed by single-point electronic structure analysis, for which we used the hybrid B3LYP functional together with the popular 6-31G(d) basis set. Table 1 presents a comparison between simulated l max using different functionals and experimental l max for TPA-AC3.…”

“…Previously, we performed theoretical studies on the structural, electronic, and optical features of two TPA organic dyes, C206 and C217, at the TiO 2 interface by performing DFTB, DFT, and TDDFT calculations. [56] A (TiO 2 ) 46 nanocluster, obtained by appropriately "cutting" an anatase slab to expose the majority (101) surface, [57] is used to model the TiO 2 nanoparticle. Reasonable results which are consistent with experimental data were obtained, thus confirming the adequacy of the proposed theoretical models for describing the dye/TiO 2 electronic properties.…”

“…The effects of acene units on the spectra and electrochemical properties of the acene-modified TPA organic dyes are demonstrated. The dye/(TiO 2 ) 46 anatase nanoparticle systems are also simulated to show the electronic structures at the interface. The results show that from TPA-AC1 to TPA-AC5 with increasing sizes of the acenes, the absorption and fluorescence spectra are systematically broadened and red-shifted, but the oscillator strength and electron injection properties are reduced.…”

“…The dye/(TiO 2 ) 46 anatase nanocluster systems were also simulated to show the electronic structures at the interface. It is expected that the investigation of intramolecular charge transfer, absorption and fluorescence spectra, and electron injection processes can give deep insight into the effects of acene units on the DSSC performance, and assist the molecular design of new and more efficient TPA-based organic dyes for the optimization of the DSSCs.…”