QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.

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Li2MnSiO4 has been identified recently as one of the first cathode battery materials that, at least in principle, could exchange more than 1 lithium per redox-active transition metal ion. In this article, we analyze experimentally and by computer simulations based on density functional theory (DFT) why actual experiments have not confirmed these expectations. We show that Li2MnSiO4 is unstable upon delithiation, with a strong tendency to amorphize. Detailed DFT calculations further indicate that it might be possible to obtain a stable material with a reversible exchange of more than one Li per formula unit (FU) by using an appropriate Mn/Fe mixture (solid solution) with a general formula Li2Mn x Fe1 - x SiO4.

Three corrosion inhibitors for copper-3-amino-1,2,4-triazole (ATA), benzotriazole (BTAH), and 1-hydroxybenzotriazole (BTAOH)-were investigated by corrosion experiments and atomistic computer simulations. The trend of corrosion inhibition effectiveness of the three inhibitors on copper in near-neutral chloride solution is determined experimentally as BTAH ≳ ATA ≫ BTAOH. A careful analysis of the results of computer simulations based on density functional theory allowed to pinpoint the superior inhibiting action of BTAH and ATA as a result of their ability to form strong N-Cu chemical bonds in deprotonated form. While these bonds are not as strong as the Cl-Cu bonds, the presence of solvent favors the adsorption of inhibitor molecules onto the surface due to stronger solvation of the Cl(-) anions. Moreover, benzotriazole displays the largest affinity among the three inhibitors to form intermolecular aggregates, such as [BTA-Cu](n) polymeric complex. This is another factor contributing to the stability of the protective inhibitor film on the surface, thus making benzotriazole an outstanding corrosion inhibitor for copper. These findings cannot be anticipated on the basis of inhibitors' molecular electronic properties alone, thus emphasizing the importance of a rigorous modeling of the interactions between the components of the corrosion system in corrosion inhibition studies.

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A low-coverage gas-phase adsorption of three corrosion inhibitors-3-amino-1,2,4-triazole (ATA), benzotriazole (BTAH), and 1-hydroxybenzotriazole (BTAOH)-on perfect Cu(111) surface has been studied and characterized using density functional theory calculations. We find that the molecules in neutral form chemisorb weakly to the perfect surface in an upright geometry. The strength of the chemisorption increases in the order BTAH < BTAOH < ATA with adsorption energies of -0.40, -0.53, and -0.60 eV, respectively. The molecules bond to the surface with triazole nitrogen atoms and also through X-H···Metal hydrogen bonds (X = N or O). In addition to chemisorption, BTAH and BTAOH can also physisorb with the molecular plane being nearly parallel to the surface and the energies of the physisorption are -0.72 and -0.97 eV, respectively, hence being more exothermic than the corresponding chemisorption energies. On the other hand, the molecules in dehydrogenated form chemisorb strongly to the surface and the strength of the chemisorption increases in the order BTAO· < ATA· < BTA· with the adsorption energies of -1.65, -2.22, and -2.78 eV, respectively. This order is compatible with the trend of experimentally observed corrosion inhibition effectiveness on copper in near-neutral chloride solutions. Although the calculations are performed at the metal/vacuum interface, they provide enough insight to rationalize why in some experiments the BTAH was observed to be adsorbed with an upright geometry and in the others with parallel geometry.

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