Motoi Tobita's research while affiliated with University of Florida and other places
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Publications (8)
The formalisms and computer implementation of size-extensive, highly accurate models of electronic structure of polymers that were CCSD, LCCSD, QCISD, CCD, LCCD, ACCD, MBPT(2) and MBPT(3) were discussed. The convergence of the correlation energies reflected the electronic structure such as the degree of π-electron conjugation. It was found that the...
Calculated vertical excitation energies, optimized geometries, and vibrational frequencies of the nitric oxide dimer are reported. The “multireference” (MR) nature of the problem and weak bond between the monomers make a proper description of the system difficult, and standard methods are not as applicable to this system. In this study, recently de...
A formalism for the analytical total energy gradient for Gaussian basis set Hartree-Fock and DFT for periodic systems, with particular emphasis on the applications to two-dimensional systems is given. As such, the formulas include energy gradients with respect to both atomic positions and lattice parameters and the contributions thereof from both s...
This dissertation is focused on the development of highly accurate electron-correlation methods for one- and two-dimensional periodic systems. For one-dimensional systems, atomic-orbital based many-body perturbation theory and coupled cluster theory are developed and applied to polyacetylene and lithiumhydride model chain. Use of atomic orbitals in...
Computational Methods ..............................................................................................................7 Molecular Description.................................................................................................................8 N 2 + Dh 2 S g (B3LYP/aug-cc-pVDZ) ................................................
A series of accurate and size-extensive ab initio wavefunction-based methods, i.e., coupled-cluster (CCD, CCSD, LCCD, ACCD, QCISD, and LCCSD) and many-body perturbation theories [MBPT(2) and MBPT(3)], are formulated and implemented for infinitely extended one-dimensional lattices (polymers), by taking account of the periodic boundary conditions. We...
The electronic and structural properties of the ground and excited states of infinite polydiacetylene chains in acetylenic PDA and butatrienic PBT structures are studied by a series of ab initio crystalline orbital and linear-combination-of-atomic-orbital periodic density functional theory methods. A complete geometry optimization is performed for...
Our focus in this paper is twofold. First, minimum structures associated with the number of imaginary frequencies at the point are searched using DFT with PW91 and B3LYP functional and coupled cluster single, double, and noniterative triple method (CCSD(T)). These calculations would give the best possible description of the PES for N6 isomers. How...
Citations
... [74,75,86,87]. We emphasize that weight derivatives of the DFT part are of great importance for the stress tensor [86,88] and consequently always included based on Refs. [74,87]. ...
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... Among these, the most salient may be hexazine, all nitrogen analog 196 of benzene; hexazine is to polyazene as benzene is to polyacetylene. Previous computational studies 180,184,[186][187][188] (with the exception of Ref. 185) indicated that its planar D 6h structure is a saddle point on its potential energy surface and is, therefore, unstable either towards dissociation into N 2 (without an activation barrier 197 ) or towards structural relaxations. Lauderdale et al. 180 showed that it has an out-of-plane bending vibration with an imaginary frequency and thus spontaneously transforms to either a twist or boat structure and eventually to hexaazaprismane (which is bound by N-N single bonds). ...
Reference: Helical organic and inorganic polymers
... The over-prediction of the kinetics for HS + O 2 reaction by using single reference method (G2) as compared to a multireference method (MRCI + Davidson) is already discussed in Section 3.3.4 . Some studies have compared the single reference and multireference methods [348][349][350] , and for the molecular systems studied, the general conclusion has been that the multireference methods work better than the single reference methods, and among the single reference methods, the coupled cluster methods like UCCSD(T) work better as compared to others. ...
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... The fundamental bandgap and related band structures are valuable targets of coupled-cluster (CC) theory, its many body perturbation theory (MBPT) approximations, and Equation of Motion-Coupled Cluster (EOM-CC) variants for polymers 1,2 and crystalline solids. [3][4][5][6] For infinite systems, only size-extensive methods 7 are capable of correctly describing electron correlation effects. These methods are similarly efficacious when transitioning from finite oligomers toward infinite, periodic systems. ...
... See Supplemental Material [21], which includes Refs. [13,[28][29][30][31][32][33][34][35][36], for numerical results confirming that lim q→0 T rCCD i ðqÞ ¼ −1=2. We complement the above discussion by numerically studying the rCCD transition structure factor and its individual diagrammatic contributions [37] given by ...
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... The computational expense of quantum chemistry methods can rise sharply with respect to the system size. For example, in coupled cluster singles and doubles (CCSD) calculations, the computational cost scaling is OðN 6 k Þ in real-space implementations [9] and OðN 4 k Þ in reciprocal-space implementations [30]. Therefore, even moderate-sized calculations with N k ¼ 2 × 2 × 2 or 3 × 3 × 3 can already be computationally challenging. ...
... In this work, 19 nitrogen atomics clusters are studied by both the MBE and IMBE to assess the performance of the IMBE approach. These clusters are obtained from Ref. [45] and their structure are presented in FIG. 2. The energies of these clusters are calculated at the level of B3LYP/aug-cc-pVTZ. All ab initio calculations are performed by Gaussian 09 software [46]. ...
