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.

The first two steps of methane dissociation on Rh(111) have been investigated using density-functional theory, focusing on the dependence of the catalyst's reactivity on the atomic coordination of the active metal site. We find that, although the barrier for the dehydrogenation of methane (CH4 --> CH3 + H) decreases as expected with the coordination of the binding site, the dehydrogenation of methyl (CH3 --> CH2 + H) is hindered at an ad-atom defect, where the first reaction is instead most favored. Our findings indicate that, if it were possible to let the dissociation occur selectively at ad-atom defects, the reaction could be blocked after the first dehydrogenation step, a result of high potential interest for many dream reactions such as, for example, the direct conversion of methane to methanol.

The chemisorption of methylchloride (CH3Cl) on Si(100) is studied from first principles. We find that, among a number of possible adsorption configurations, the lowest-energy structure is one in which the methylchloride molecule is dissociated into CH3 and Cl fragments which are bound to the two Si atoms of the same surface dimer. Our calculations show that dissociative chemisorption of methylchloride on Si(100) may proceed along different reaction paths characterized by different energy barriers that the system must overcome: some dissociation processes are mediated by a molecular precursor state and, at least in one case, we find that the dissociation process is nonactivated, in agreement with recent experimental findings. We have also generated, for many possible adsorption structures, theoretical scanning tunneling microscopy images which could facilitate the interpretation of experimental measurements.