2,341 research outputs found
Cluster expansion of multicomponent ionic systems with controlled accuracy: Importance of long-range interactions in heterovalent ionic systems
We have been examining factors determining the accuracy of cluster expansion
(CE), which is used in combination with many density functional theory (DFT)
calculations. With the exception of multicomponent metallic or isovalent ionic
systems, the contributions of long-range effective cluster interactions (ECIs)
to configurational energetics are not negligible, which is ascribed to
long-range electrostatic interactions. The truncation of ECIs in such systems
leads to systematic errors. A typical problem with such errors can be seen in
Monte Carlo (MC) simulations since simulation supercells composed of a larger
number of atoms than those of the input DFT structures are used. The prediction
errors for long-period structures beyond the cell size of the input DFT
structures in addition to those for short-period structures within the cell
size of the input DFT structures need to be carefully examined to control the
accuracy of CE. In the present study, we quantitatively discuss the
contribution of the truncation of long-range ECIs to the accuracy of CE. Two
types of system, namely, a point-charge spinel lattice and a real MgAl2O4
spinel crystal, are examined
Property Taxation and the Demand for Floor Space in Japan
This is the first study applying the econometric analysis of piecewise-linear budget constraints arising from space-linked property taxation to Japanese housing data. The model employed is the classical Hausman type with convex piecewise-linear budget constraints and fixed preferences. We estimate that if spaced-linked property taxation for newly built houses is abolished, it would then eliminate a current excess tax burden per household of approximately 25,000 yen.Nonlinear budget constraints, Property taxation, Housing demand, Floor space, Japan
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
First-principles interatomic potentials for ten elemental metals via compressed sensing
Interatomic potentials have been widely used in atomistic simulations such as
molecular dynamics. Recently, frameworks to construct accurate interatomic
potentials that combine a systematic set of density functional theory (DFT)
calculations with machine learning techniques have been proposed. One of these
methods is to use compressed sensing to derive a sparse representation for the
interatomic potential. This facilitates the control of the accuracy of
interatomic potentials. In this study, we demonstrate the applicability of
compressed sensing to deriving the interatomic potential of ten elemental
metals, namely, Ag, Al, Au, Ca, Cu, Ga, In, K, Li and Zn. For each elemental
metal, the interatomic potential is obtained from DFT calculations using
elastic net regression. The interatomic potentials are found to have prediction
errors of less than 3.5 meV/atom, 0.03 eV/\AA\ and 0.15 GPa for the energy,
force and the stress tensor, respectively, which enable the accurate prediction
of physical properties such as lattice constants and the phonon dispersion
relationship.Comment: 11 pages, 5 figure
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