863 research outputs found
Efficient determination of alloy ground-state structures
We propose an efficient approach to accurately finding the ground-state
structures in alloys based on the cluster expansion method. In this approach, a
small number of candidate ground-state structures are obtained without any
information of the energy. To generate the candidates, we employ the convex
hull constructed from the correlation functions of all possible structures by
using an efficient algorithm. This approach is applicable to not only simple
lattices but also complex lattices. Firstly, we evaluate the convex hulls for
binary alloys with four types of simple lattice. Then we discuss the structures
on the vertices. To examine the accuracy of this approach, we perform a set of
density functional theory calculations and the cluster expansion for Ag-Au
alloy and compare the formation energies of the vertex structures with those of
all possible structures. As applications, the ground-state structures of the
intermetallic compounds CuAu, CuAg, CuPd, AuAg, AuPd, AgPd, MoTa, MoW and TaW
are similarly evaluated. Finally, the energy distribution is obtained for
different cation arrangements in MgAlO spinel, for which long-range
interactions are essential for the accurate description of its energetics.Comment: 8 pages, 7 figure
Nonequilibrium transport on a quantum molecular chain in terms of the complex Liouvillian spectrum
The transport process in a molecular chain in a nonequilibrium stationary state is theoretically investigated. The molecule is interacting at both ends with thermal baths of different temperatures, while no dissipation mechanism is contained inside the molecular chain. We have first obtained the nonequilibrium stationary state outside the Hilbert space in terms of the complex spectral representation of Liouvillian. The nonequilibrium stationary state is obtained as an eigenstate of the Liouvillian, which is constructed through the collision invariant of the kinetic equation. The eigenstate of the Liouvillian contains information on the spatial correlation between the molecular chain and the thermal baths. While energy flow in the nonequilibrium state which is due to the first-order correlation can be described by the Landauer formula, the particle current due to the second-order correlation cannot be described by the Landauer formula. The present method provides a simple way to evaluate the energy transport in a molecular chain in a nonequilibrium situation.Ministry of Education, Science, Sports, and Culture of JapanYukawa International Program for Quark-Hadron Sciences YIPQSPhysic
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