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In this work, it is shown that for the first time that, using information-entropy-based methods, one can quantitatively explore the relative impact of a wide multidimensional array of electronic and chemical bonding parameters on the structural stability of intermetallic compounds. Using an inorganic AB(2) compound database as a template data platform, the evolution of design rules for crystal chemistry based on an information-theoretic partitioning classifier for a high-dimensional manifold of crystal chemistry descriptors is monitored. An application of this data-mining approach to establish chemical and structural design rules for crystal chemistry is demonstrated by showing that, when coupled with first-principles calculations, statistical inference methods can serve as a tool for significantly accelerating the prediction of unknown crystal structures.

The crystal structure of iron, the major component of the Earth's inner core (IC), is unknown for the IC high pressure (P; 3.3-3.6 Mbar) and temperature (T; 5000-7000 K). There is mounting evidence that the hexagonal close-packed (hcp) phase of iron, stable at the high P of the IC and a low T, might be unstable under the IC conditions due to the impact of high T and impurities. Experiments at the IC P and T are difficult and do not provide a conclusive answer as regards the iron stability at the pressure of the IC and temperatures close to the iron melting curve. Recent theory provides contradictory results regarding the nature of the stable Fe phase. We investigated the possibility of body-centered cubic (bcc) phase stabilization at the P and T in the vicinity of the Fe melting curve by using ab initio molecular dynamics. Thermodynamic calculations, relying on the model of uncorrelated harmonic oscillators, provide nearly identical free energies within the error bars of our calculations. However, direct simulation of iron crystallization demonstrates that liquid iron freezes in the bcc structure at the P of the IC and T = 6000 K. All attempts to grow the hcp phase from the liquid failed. The mechanism of bcc stabilization is explained. This resolves most of the earlier confusion.

Lattice dynamical methods used to predict phase transformations in crystals typically deal with harmonic phonon spectra and are therefore not applicable in important situations where one of the competing crystal structures is unstable in the harmonic approximation, such as the bcc structure involved in the hcp-to-bcc martensitic phase transformation in Ti, Zr and Hf. Here we present an expression for the free energy that does not suffer from such shortcomings, and we show by self-consistent ab initio lattice dynamical calculations (SCAILD), that the critical temperature for the hcp-to-bcc phase transformation in Ti, Zr and Hf, can be effectively calculated from the free-energy difference between the two phases. This opens up the possibility to study quantitatively, from first-principles theory, temperature-induced phase transitions.

We study exciton states in a coupled double quantum well (CDQW) semiconductor structure. Exciton levels and binding energies of direct and indirect excitons are calculated for a symmetric CDQW system with an applied electric field. The exciton states are obtained by solving the exciton effective-mass equation in the momentum space using the modified Gaussian quadrature method. Within this approach we perform realistic calculations of the exciton states by taking into account the coupling between different subband pairs and calculate optical-absorption coefficients. The calculated values of the exciton binding energy are in a good agreement with the experiment and the calculated absorption spectra qualitatively agree with the measured photoluminescence excitation spectra.

Boundary roughness scattering in disordered tunnel-coupled quantum wires in the presence of a magnetic

field is considered. The low-temperature conductance as a function of applied magnetic field is calculated for

different structure and disorder parameters using the method of the generalized S-matrix composition.We show

that despite the fact that lateral wire width fluctuations of the size of few atomic layers may significantly shift

the partial energy gap, the effect of the conductance enhancement at energies in the partial energy gap does

take place in sufficiently strong magnetic fields and small correlation length of the disorder defined as the

average distance between the neighboring discontinuities of the boundary profile. The last parameter is shown

to be particularly important for the determination of the transport properties of the system. Remarkably, we find

that in a wide range of system parameters the conductance decreases with the correlation length despite the

decreasing number of boundary discontinuities.

We investigate the effect of the boundary roughness scattering on the conductance of a disordered tunnel-coupled quantum wire in the presence of a magnetic field. It is shown that the average distance between the neighboring discontinuities of the boundary profile plays an important role in the transport properties of the system and the manifestation of the localization-delocalization effect. Present studies point out a new effect consisting in the

decrease of the conductance with the increase of the disorder correlation length.