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In this study, bandgap of the two‐dimensional (2D) TiO2, a transition‐metal oxide, was obtained by the diffusion Monte Carlo (DMC) method for the first time. This genuine 2D monolayer material that includes transition elements has been proven to be very challenging for reliable prediction of the bandgap. In order to improve the description of correlation effects, the DMC method was used to calculate the bandgaps of 2D‐TiO2 in α‐ and β‐phases, and the obtained results were compared with the density functional theory (DFT) calculations. The DMC results obtained from the infinite periodic superlattices predict ∆f of the 2D‐TiO2 in the α‐ and β‐phases to be about 5.54(4) and 5.69(2) eV, respectively, indicating that the available DFT results significantly underestimated the bandgaps of 2D‐TiO2 nanosheets. Considering the recently reported linear scaling relationship between the bandgap ∆f and the exciton binding energy ∆e of 2D semiconductors, (∆e ≈ 0.28∆f), the optical bandgap ∆o was further predicted to be ~3.99 eV for the α‐phase TiO2, and it is consistent with the experimental value (~3.84 eV). The successful application of the quantum Monte Carlo (QMC) method on the 2D‐TiO2 systems implies that QMC may serve as a feasible tool to investigate the electronic properties of the freestanding 2D transition‐metal oxides. [ABSTRACT FROM AUTHOR]

Bond dissociation energies (BDEs) for some nitro or amino contained prototypical molecules in energetic materials are computed by fixed-node diffusion quantum Monte Carlo method. The nodes are determined from a Slater determinant calculated within density functional theory at the B3LYP/6-311G** level. The possible errors, the nodal error, and the cancellation of nodal errors in calculating BDE are discussed, and the accuracy is compared with other available ab initio computations and experimental results. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Maximum capacities of the hydrogen storage in organometallic compounds consisting of Co and Ni atoms bound to C mH m ring ( m = 4, 5; capped type) were, respectively, found as 3.48 and 3.49 wt % (Guo et al., Struct Chem, 2009, 20, 1107). Here, we extend this study to structures having a transition metal (TM) inserted in C mH m ring (inserted type), having TM located on either a C4H [ABSTRACT FROM AUTHOR]

Density functional theory calculation was carried out on cation-π complexes formed by cations [M = H+, Li+, Na+, K+, Be2+, Mg2+, and Ca2+] and π systems of annelated benzene. The cation-π bonding energy of Be2+ or Mg2+ with annelated benzene is very strong in comparison with the common cation-π intermolecular interaction, and the bonding energies follow the order Be2+ > Mg2+ > Ca2+ > Li+ > Na+ > K+. Similarly, the interaction energies follow the trend 1-M < 2-M < 3-M for all the metal cations considered. These outcomes may be due to the weak interactions of the metal cations with C&bond;H and the interactions of metal cations with π in addition to the nature of a metal cation. We have also investigated on all the possible substituted sites, and find that the metal ion tends to interact with all ring atoms while proton prefers to bind covalently to one of the ring carbons. The binding of metal cations with annelated benzenes has striking effect on nuclear magnetic resonance chemical shifts using the gauge independent atomic orbital method. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]

The properties of 2-Nitrimino-1-nitroimidazolidine are calculated by using SIESTA code, which adopts the standard Kohn-Sham self-consistent density functional method in the local density approximation. The structures and electronic properties are analyzed, and the factors that affect the impact sensitivity are discussed based on the crystal structure, band energy, and projected density of state. The reason for the smaller impact sensitivity compared to RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) is also explored from several respects such as the weakest bond dissociation energy in single molecule, and hydrogen bond, band gap in the crystal. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [ABSTRACT FROM AUTHOR]