Predicting solid-state heats of formation of newly synthesized polynitrogen materials by using quantum mechanical calculations.

We present density functional theory level predictions and analysis of the basic properties of newly synthesized high-nitrogen compounds together with 3,6-bis(2H-tetrazol-5-yl)-1,2,4,5-tetrazine (BTT) and 3,3'-azobis(6-amino-1,2,4,5-tetrazine) (DAAT), for which experimental data are available. The newly synthesized high-nitrogen compounds are based on tricycle fused 1,2,4-triazine and 1,2,4,5-tetrazine heterocycles. In this work, the molecules BTT and DAAT have been studied in order to validate the theoretical approach and to facilitate further progress developments for the molecules of interest.

The peculiar electronic structure of PbSe quantum dots.

PbSe is a pseudo-II-VI material distinguished from ordinary II-VI's (e.g., CdSe, ZnSe) by having both its valence band maximum (VBM) and its conduction band minimum (CBM) located at the fourfold-degenerate L-point in the Brillouin zone.

Systematic method to new phases of polymeric nitrogen under high pressure.

A systematic method to unravel a large class of single-bonded (SB) polymeric phases of nitrogen under high pressure is presented. The approach is based on the combinatorial generation of different Peierls-like distortions of a given reference structure that maintain the threefold connectivity of SB nitrogen, followed by first-principles calculations. Using an eight atom simple cubic reference structure, the approach not only recovers all four SB nitrogen phases reported to date, but eight new metastable structures (confirmed by phonon density of states calculations) are found.

First-principles combinatorial design of transition temperatures in multicomponent systems: the case of Mn in GaAs.

The transition temperature TC of multicomponent systems--ferromagnetic, superconducting, or ferroelectric--depends strongly on the atomic arrangement, but an exhaustive search of all configurations for those that optimize TC is difficult, due to the astronomically large number of possibilities. Here we address this problem by parametrizing the TC of a set of approximately 50 input configurations, calculated from first principles, in terms of configuration variables ("cluster expansion"). Once established, this expansion allows us to search almost effortlessly the transition temperature of arbitrary configurations.

Searching for alloy configurations with target physical properties: impurity design via a genetic algorithm inverse band structure approach.

The ability to artificially grow different configurations of semiconductor alloys--random structures, spontaneously ordered and layered superlattices--raises the issue of how different alloy configurations may lead to new and different alloy physical properties. We address this question in the context of nitrogen impurities in GaP, which form deep levels in the gap whose energy and optical absorption sensitively depend on configuration. We use the "inverse band structure" approach in which we first specify a desired target physical property (such as the deepest nitrogen level, or lowest strain configuration), and then we search, via genetic algorithm, for the alloy atomic configurations that have this property.