A two-level hierarchical parallelization scheme including the second-order Moller-Plesset perturbation (MP2) theory in the divide-and-conquer method is presented. The scheme is a combination of coarse-grain paralleliz...
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A two-level hierarchical parallelization scheme including the second-order Moller-Plesset perturbation (MP2) theory in the divide-and-conquer method is presented. The scheme is a combination of coarse-grain parallelization assigning each subsystem to a group of processors, with fine-grain parallelization, where the computational tasks for evaluating MP2 correlation energy of the assigned subsystem are distributed among processors in the group. Test calculations demonstrate that the present scheme shows high parallel efficiency and makes MP2 calculations practical for very large molecules. (C) 2011 Wiley Periodicals, Inc. J Comput Chem 32: 2756-2764, 2011
The divide-and-conquer (DC) method, which is one of the linear-scaling methods avoiding explicit diagonalization of the Fock matrix. has been applied mainly to pure density functional theory (DFT) or semiempirical mol...
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The divide-and-conquer (DC) method, which is one of the linear-scaling methods avoiding explicit diagonalization of the Fock matrix. has been applied mainly to pure density functional theory (DFT) or semiempirical molecular orbital calculations so far. The present study applies the DC method to such calculations including the Hartree-Fock (HF) exchange terms as the HF and hybrid HF/DFT. Reliability of the DC-HF and DC-hybrid HF/DFT is found to be strongly dependent oil the cut-off radius, which defines the localization region in the DC formalism. This dependence on the cut-off radius is assessed from various points of view: that is, total energy, energy components, local energies, and density of states. Additionally, to accelerate the self-consistent field convergence in DC calculations, a new convergence technique is proposed. (c) 2007 Wiley, Periodicals, Inc.
Recently, we applied Yang's divide-and-conquer (DC) method to the Hartree-Fock (HF) and hybrid density functional theories and assessed its reliability in calculations of bond-alternating polyene chains. In this p...
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Recently, we applied Yang's divide-and-conquer (DC) method to the Hartree-Fock (HF) and hybrid density functional theories and assessed its reliability in calculations of bond-alternating polyene chains. In this paper, we investigate the cut-off behaviour of the HF exchange interaction in the DC-HF method by comparing the results of bond-alternating polyene chains with those of more delocalized uniform polyene chains. The cut-off error of the uniform chain is much larger than that of the bond-alternating chain because of the delocalized electronic structure of the uniform polyene chain. We also estimate the exponential decay coefficient of the cut-off error in the DC scheme and compare it with that of the real-space one-particle density matrix, which can be represented by the band gap in the insulator limit. It can be concluded that the cut-off derived from the DC-HF method can be reduced to an arbitrary magnitude of error by adopting an appropriate buffer radius corresponding to the band gap.
The application of conventional ab initio methods to large high-spin systems remains challenging because CPU time rapidly increases with the system size. The unrestricted elongation method performs stepwise electronic...
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The application of conventional ab initio methods to large high-spin systems remains challenging because CPU time rapidly increases with the system size. The unrestricted elongation method performs stepwise electronic structure calculations for large high-spin systems and can reproduce the results of conventional methods, i.e., achieve a very small total energy error (similar to 10(-9) a.u. per atom). Moreover, a polarizable continuum model (PCM) method is incorporated for the estimation of solvent effect and it is demonstrated that the unrestricted PCM-elongation method is accurate and efficient for performing electronic structure calculations of large high-spin systems under solvent.
Water aggregates allow for numerous configurations due to different distributions of hydrogen bonds. The total number of possible hydrogen-bond networks is very large even for medium-sized systems. We demonstrate that...
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Water aggregates allow for numerous configurations due to different distributions of hydrogen bonds. The total number of possible hydrogen-bond networks is very large even for medium-sized systems. We demonstrate that targeted ultrafast methods of quantum chemistry make an exhaustive analysis of all configurations possible. The cage of (H2O)(20) in the form of the pentagonal clodecahedron is a common motif in water structures. We calculated the spatial and electronic structure of all hydrogen-bond configurations for three systems: idealized cage (H2O)(20) and defect cages with one or two hydrogen bonds broken. More than 3 million configurations studied provide unique data on the structure and properties of water clusters. We performed a thorough analysis of the results with the emphasis on the cooperativity in water systems and the structure-property relations.
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