Theoretical Aspects in Realization of Functional Nanoporous Material

In order to design materials with novel composition and desirable characteristics it is important to have a good understanding of the atomic-scale chemical and physical properties of materials. Using powerful computer system installed in Institute for Materials Research, Tohoku University and effective simulation methods we try to accurately estimate the important properties of various complex materials in order to accelerate the realization of novel materials, hand-in-hand with experiment and propose these materials for various applications. Here, the recent achievements of our group have been reviewed. Formalism for calculating the thermodynamic properties of a clathrate hydrate with weak guest-host interactions was realized for energy storage applications. The proposed model accounted for multiple cage occupancy, host lattice relaxation, and the description of the quantum nature of guest behavior [1]. Using this approach, the phase diagrams of various hydrates was constructed and they are in agreement with available experimental data [2-5]. In order to evaluate the parameters of weak interactions, a time-dependent density-functional formalism and local density technique entirely in real space have been implemented for calculations of vdW dispersion coefficients for atoms within the all-electron mixed-basis approach [6]. The combination of both methods enables one to calculate thermodynamic properties of clathrate hydrates without resorting to any empirical parameter fittings. Using the proposed method it is possible not only confirm the existing experimental data but also predict the unknown region of thermodynamic stability of clathrate hydrates, and also propose the gas storage ability as well as the gas composition for which high-stability region of clathrate hydrates can be achieved. The proposed method is quite general and can be applied to the various nanoporous compounds with weak guest-host interactions. We have also shown in collaboration with experimentalists that the concept using a designable regular MOF material could be applicable to a highly stable, selective adsorption system [7-9]. Thus, the high sorption ability of a specific metal-organic framework (MOF) for acetylene from a CO2/C2H2 gas mixture is demonstrated [7]. The high selectivity of CO has been achieved from a mixture with nitrogen by both the local interaction between CO and accessible Cu2+ metal sites and the modification of nanopore size [8]. The synthesis of MOF with the urotropine moiety can significantly improve the selective adsorption of C2H2 and CO2 gases [9]. R. V. Belosludov et al. Mater. Trans. 48 704 (2007) R. V. Belosludov et al. J. Chem. Phys.131 (2009) 244510. R. V. Belosludov et al. Mol. Simul. 38 (2012) 773. R. V. Belosludov et al. J. Phys. Chem. C 118 (2014) 2587. R. V. Belosludov et al. J. Renew. Sust. Energy,6 (2014), 053132. R. V. Belosludov et al. in Handbook of Sustainable Engineering, ed. by K-M. Lee and J. Kauffman, Springer, New York, (2013) pp. 1215-1247. 7. R. Matsuda et al. Nature 436 238 (2005). H. Sato et al. Science 343 (2014) 167. A. Sapchenko et al., Chem. Comm. 51 (2015) 13918

Influence of molecular geometry, exchange-correlation functional, and solvent effects in the modeling of vertical excitation energies in phthalocyanines using time-dependent density functional theory (TDDFT) and polarized continuum model TDDFT methods: can modern computational chemistry methods explain experimental controversies?

A time-dependent density functional theory (TDDFT) approach coupled with 14 different exchange-correlation functionals was used for the prediction of vertical excitation energies in zinc phthalocyanine (PcZn). In general, the TDDFT approach provides a more accurate description of both visible and ultraviolet regions of the UV-vis and magnetic circular dichroism (MCD) spectra of PcZn in comparison to the more popular semiempirical ZINDO/S and PM3 methods. It was found that the calculated vertical excitation energies of PcZn correlate with the amount of Hartree-Fock exchange involved in the exchange-correlation functional. The correlation was explained on the basis of the calculated difference in energy between occupied and unoccupied molecular orbitals. The influence of PcZn geometry, optimized using different exchange-correlation functionals, on the calculated vertical excitation energies in PcZn was found to be relatively small. The influence of solvents on the calculated vertical excitation energies in PcZn was considered for the first time using a polarized continuum model TDDFT (PCM-TDDFT) method and was found to be relatively small in excellent agreement with the experimental data. For all tested TDDFT and PCM-TDDFT cases, an assignment of the Q-band as an almost pure a_(1u) (HOMO)-->e_g (LUMO) transition, initially suggested by Gouterman, was confirmed. Pure exchange-correlation functionals indicate the presence of six ^1_Eu states in the B-band region of the UV-vis spectrum of PcZn, while hybrid exchange-correlation functionals predict only five ^1E_u states for the same energy envelope. The first two symmetry-forbidden n-->pi* transitions were predicted in the Q0-2 region and in the low-energy tail of the B-band, while the first two symmetry-allowed n-->π* transitions were found within the B-band energy envelope when pure exchange-correlation functionals were used for TDDFT calculations. The presence of a symmetry-forbidden but vibronically allowed n-->π* transition in the Q_(0-2) spectral envelope explains the long-time controversy between the experimentally observed low-intensity transition in the Q_(0-2) region and previous semiempirical and TDDFT calculations, which were unable to predict any electronic transitions in this area. To prove the conceptual possibility of the presence of several degenerate ^1E_u states in the B-band region of PcZn, room-temperature UV-vis and MCD spectra of zinc tetra-tert-butylphthalocyanine (Pc^tZn) in non-coordinating solvents were recorded and analyzed using band deconvolution analysis. It was found that the B-band region of the UV-vis and MCD spectra of Pc^tZn can be easily deconvoluted using six MCD Faraday A-terms and two MCD Faraday B-terms with energies close to those predicted by TDDFT calculations for ^1E_u and ^1A_(2u) excited states, respectively. Such a good agreement between theory and experiment clearly indicates the possibility of employing a TDDFT approach for the accurate prediction of vertical excitation energies in phthalocyanines within a large energy range

Modeling of dielectric function of YBa2Cu3O7 and Tl2CaBa2Cu2O8 with lattice dynamics approach.

High temperature superconductivity : new materials and properties : joint symposium of the SB RAS and the CNEAS TU / edited by Kyosuke Terayam