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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(More)
The structure of self-assembled monolayers (SAMs) of long-chain alkyl sulfides on gold(111) has been resolved by density functional theory-based molecular dynamics simulations and grazing incidence x-ray diffraction for hexanethiol and methylthiol. The analysis of molecular dynamics trajectories and the relative energies of possible SAM structures suggest a(More)
We carry out an ab initio study of the structural, electronic, and magnetic properties of zigzag graphene nanoribbons on Cu(111), Ag(111), and Au(111). Both, H-free and H-terminated nanoribbons are considered revealing that the nanoribbons invariably possess edge states when deposited on these surfaces. In spite of this, they do not exhibit a significant(More)
The study of metal-insulator transitions (MITs) in crystalline solids is a subject of paramount importance, both from the fundamental point of view and for its relevance to the transport properties of materials. Recently, a MIT governed by disorder was observed in crystalline phase-change materials. Here we report on calculations employing density(More)
Using low-temperature scanning tunneling spectroscopy, we map the local density of states of graphene quantum dots supported on Ir(111). Because of a band gap in the projected Ir band structure around the graphene K point, the electronic properties of the QDs are dominantly graphenelike. Indeed, we compare the results favorably with tight binding(More)
Despite its simple chemical constitution and unparalleled technological importance, the phase-change material germanium telluride (GeTe) still poses fundamental questions. In particular, the bonding mechanisms in amorphous GeTe have remained elusive to date, owing to the lack of suitable bond-analysis tools. Herein, we introduce a bonding indicator for(More)
We computed the Raman spectrum of amorphous GeTe by ab initio simulations and empirical bond polarizability models. The calculated spectrum is in very good agreement with experimental data and contains the signatures of all the peculiar local structures of the amorphous phase revealed by recent ab initio simulations, namely, tetrahedral Ge and defective(More)
Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between the amorphous and crystalline state that display large differences in electrical and optical properties. In addition to the amorphous-to-crystalline transition, experimental results on polycrystalline(More)
Aging is a ubiquitous phenomenon in glasses. In the case of phase-change materials, it leads to a drift in the electrical resistance, which hinders the development of ultrahigh density storage devices. Here we elucidate the aging process in amorphous GeTe, a prototypical phase-change material, by advanced numerical simulations, photothermal deflection(More)
The zigzag edges of graphene on Ir(111) are studied by ab initio simulations and low-temperature scanning tunneling spectroscopy, providing information about their structural, electronic, and magnetic properties. No edge state is found to exist, which is explained in terms of the interplay between a strong geometrical relaxation at the edge and a(More)