An adaptive algorithm for n-body field expansions
Weinberg, Martin D.
1998-05-28
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38 records were found.
Comment: 8 pages, with 3 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/lh_dw/index.html
Comment: 4 pages, with 3 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/lh_wann/index.html
"Risk management" in securities markets refers to the oversight of portfolio managers and professional traders when they trade on behalf of investors in security markets. Monitoring of their trading performance, profit and loss, and risk-taking behavior, is measured by principals using security market prices. We study the optimality of the practice of marking-to-market and provide conditions under which investing principals should optimally monitor their agent traders using market prices to measure traders' performance. Asset prices, however, can be affected by mark-to-market contracts. We show that such contracts introduce an externality when there are many traders. Traders may rationally herd, trading on irrelevant information. Ironically, this causes asset prices to be less informative than they would be without the mark-to-market f...
The ground state structural, electronic and magnetic properties of
multiferroic TbMn$_2$O$_5$ are investigated via first-principles calculations.
We show that the ferroelectricity in TbMn$_2$O$_5$ is driven by the
non-centrosymmetric magnetic ordering, without invoking the spin-orbit coupling
and non-collinear spins. The {\it intrinsic} electric polarization in this
compound is calculated to be 1187 $nC\cdot$ cm$^{-2}$, an order of magnitude
larger than previously thought.
Comment: 12 pages, 5 figures
We propose a unique scheme to construct fully optimized atomic basis sets for
density-functional calculations. The shapes of the radial functions are
optimized by minimizing the {\it spillage} of the wave functions between the
atomic orbital calculations and the converged plane wave calculations for dimer
systems. The quality of the bases can be systematically improved by increasing
the size of the bases within the same framework. The scheme is easy to
implement and very flexible. We have done extensive tests of this scheme for
wide variety of systems. The results show that the obtained atomic basis sets
are very satisfactory for both accuracy and transferability.
We present an efficient scheme for accurate electronic structure
interpolations based on the systematically improvable optimized atomic
orbitals. The atomic orbitals are generated by minimizing the spillage value
between the atomic basis calculations and the converged plane wave basis
calculations on some coarse $k$-point grid. They are then used to calculate the
band structure of the full Brillouin zone using the linear combination of
atomic orbitals (LCAO) algorithms. We find that usually 16 -- 25 orbitals per
atom can give an accuracy of about 10 meV compared to the full {\it ab initio}
calculations. The current scheme has several advantages over the existing
interpolation schemes. The scheme is easy to implement and robust which works
equally well for metallic systems and systems with complex band structures.
Furthermore, the ato...
We investigate the electromagnon in magnetoferroelectrics RMn$_2$O$_5$ using
combined molecular-spin dynamics simulations. We identify the origin of the
electromagnon modes observed in the optical spectra and reproduce the most
salient features of the electromagnon in these compounds. We find that the
electromagnon frequencies are very sensitive to the magnetic wave vector along
the $a$ direction. We further investigate the electromagnon in magnetic field.
Although the modes frequencies change significant under magnetic field, the
static dielectric constant electromagnon does not change much in the magnetic
field.
