QUANTAS: a Python software for the analysis of thermodynamics and elastic behavior of solids from ab initio quantum mechanical simulations and experimental data

This paper presents QUANTAS, an open-source Python-based software aimed at providing a fast, flexible and easy-to-use framework to calculate the thermodynamics and elastic properties of crystalline solids. QUANTAS could be of use for researchers involved in various fields of solid-state chemistry, physics and mineralogy.

Mineralogy, petrology and materials science are fundamental disciplines not only for the basic knowledge and classification of solid phases but also for their technological applications, which are becoming increasingly demanding and challenging. Characterization and design of materials are of utmost importance and usually need knowledge of the thermodynamics and mechanical stability of solids. Alongside well known experimental approaches, in recent years the advances in both quantum mechanical methods and computational power have placed theoretical investigations as a complementary useful and powerful tool in this kind of study. In order to aid both theoreticians and experimentalists, an open-source Python-based software, QUANTAS, has been developed. QUANTAS provides a fast, flexible, easy-to-use and extensible platform for calculating the thermodynamics and elastic behavior of crystalline solid phases, starting from both experimental and ab initio data.

Structure and elastic properties of Mg(OH)2 from density functional theory

The structure, lattice dynamics and mechanical properties of magnesium hydroxide have been investigated by static density functional theory calculations as well as ab initio molecular dynamics. The hypothesis of a superstructure existing in the lattice formed by the hydrogen atoms has been tested. The elastic constants of the material have been calculated with a static deformations approach and are in fair agreement with the experimental data. The hydrogen subsystem structure exhibits signs of disordered behaviour while maintaining correlations between the angular positions of neighbouring atoms. We establish that the essential angular correlations between hydrogen positions are maintained to a temperature of at least 150 K and that they are well described by a physically motivated probabilistic model. The rotational degree of freedom appears to be decoupled from the lattice directions above 30 K.

Synchrotron Infrared Absorbance Measurements of Hydrogen in MgSiO 3 Perovskite

Micro-infrared spectroscopic measurements on single crystals of MgSiO(3) perovskite document two pleochroic hydroxyl absorbance peaks at 3483 and 3423 centimeter(-1). These measurements were obtained with the use of a synchrotron infrared source for spectroscopy. These data are consistent with a trace hydrogen content of 700 +/- 170 hydrogen atoms per 10(6) silicon atoms in the nominally anhydrous MgSiO(3) perovskite. When integrated over the volume of the lower mantle, this concentration is comparable to 12 percent of the mass of hydrogen in the Earth's hydrosphere.