arXiv subjects

Marco Buongiorno Nardelli

Publications and source records attributed to Marco Buongiorno Nardelli.

49 records · Page 3Linked to original sources

arXiv2015

Accurate tight-binding Hamiltonian matrices from ab-initio calculations: Minimal basis sets

Projection of Bloch states obtained from quantum-mechanical calculations onto atomic orbitals is the fastest scheme to construct ab-initio tight-binding Hamiltonian matrices. However, the presence of spurious states and unphysical hybridizations of the tight-binding eigenstates has hindered the applicability of this construction. Here we demonstrate that those spurious effects are due to the inclusion of Bloch states with low projectability. The mechanism for the formation of those effects is derived analytically. We present an improved scheme for the removal of the spurious states which results in an efficient scheme for the construction of highly accurate ab-initio tight-binding Hamiltonians.

cond-mat.mtrl-sci↗

arXiv2015

First principles thermodynamical modeling of the binodal and spinodal curves in lead chalcogenides

High-throughput ab-initio calculations, cluster expansion techniques and thermodynamic modeling have been synergistically combined to characterize the binodal and the spinodal decompositions features in the pseudo-binary lead chalcogenides PbSe-PbTe, PbS-PbTe, and PbS-PbSe. While our results agree with the available experimental data, our consolute temperatures substantially improve with respect to previous computational modeling. The computed phase diagrams corroborate that the formation of spinodal nanostructures causes low thermal conductivities in these alloys. The presented approach, making a rational use of online quantum repositories, can be extended to study thermodynamical and kinetic properties of materials of technological interest.

cond-mat.mtrl-sci↗

arXiv2015

The AFLOW Standard for High-Throughput Materials Science Calculations

The Automatic-Flow ( AFLOW ) standard for the high-throughput construction of materials science electronic structure databases is described. Electronic structure calculations of solid state materials depend on a large number of parameters which must be understood by researchers, and must be reported by originators to ensure reproducibility and enable collaborative database expansion. We therefore describe standard parameter values for k-point grid density, basis set plane wave kinetic energy cut-off, exchange-correlation functionals, pseudopotentials, DFT+U parameters, and convergence criteria used in AFLOW calculations.

cond-mat.mtrl-sci↗

arXiv2015

Improved predictions of the physical properties of Zn- and Cd-based wide band-gap semiconductors: a validation of the ACBN0 functional

We study the physical properties of Zn$X$ ($X$=O, S, Se, Te) and Cd$X$ ($X$=O, S, Se, Te) in the zinc-blende, rock-salt, and wurtzite structures using the recently developed fully $ab$ $initio$ pseudo-hybrid Hubbard density functional ACBN0. We find that both the electronic and vibrational properties of these wide-band gap semiconductors are systematically improved over the PBE values and reproduce closely the experimental measurements. Similar accuracy is found for the structural parameters, especially the bulk modulus. ACBN0 results compare well with hybrid functional calculations at a fraction of the computational cost.

cond-mat.mtrl-sci↗

arXiv2014

Formation and properties of astrophysical carbonaceous dust. I: ab-initio calculations of the configuration and binding energies of small carbon clusters

The binding energies of n < 100 carbon clusters are calculated using the ab-initio density functional theory code Quantum Espresso. Carbon cluster geometries are determined using several levels of classical techniques and further refined using density functional theory. The resulting energies are used to compute the work of cluster formation and the nucleation rate in a saturated, hydrogen-poor carbon gas. Compared to classical calculations that adopt the capillary approximation, we find that nucleation of carbon clusters is enhanced at low temperatures and depressed at high temperatures. This difference is ascribed to the different behavior of the critical cluster size. We find that the critical cluster size is at n = 27 or n = 8 for a broad range of temperatures and saturations, instead of being a smooth function of such parameters. The results of our calculations can be used to follow carbonaceous cluster/grain formation, stability, and growth in hydrogen poor environments, such as the inner layers of core-collapse supernova and supernova remnants.

astro-ph.SR↗

arXiv2014

Reformulation of DFT+U as a pseudo-hybrid Hubbard density functional

The accurate prediction of the electronic properties of materials at a low computational expense is a necessary conditions for the development of effective high-throughput quantum-mechanics (HTQM) frameworks for accelerated materials discovery. HTQM infrastructures rely on the predictive capability of Density Functional Theory (DFT), the method of choice for the first principles study of materials properties. However, DFT suffers of approximations that result in a somewhat inaccurate description of the electronic band structure of semiconductors and insulators. In this article we introduce ACBN0, a pseudo-hybrid Hubbard density functional that yields an improved prediction of the band structure of insulators such as transition-metal oxides, as shown for TiO2, MnO, NiO and ZnO, with only a negligible increase in computational cost.

cond-mat.str-el↗

arXiv2014

High-Throughput Computational Screening of thermal conductivity, Debye temperature and Grüneisen parameter using a quasi-harmonic Debye Model

The quasi-harmonic Debye approximation has been implemented within the AFLOW and Materials Project frameworks for high-throughput computational science (Automatic Gibbs Library, AGL), in order to calculate thermal properties such as the Debye temperature and the thermal conductivity of materials. We demonstrate that the AGL method, which is significantly cheaper computationally compared to the fully ab initio approach, can reliably predict the ordinal ranking of the thermal conductivity for several different classes of semiconductor materials. We also find that for the set of 182 materials investigated in this work the Debye temperature, calculated with the AGL, is often a better predictor of the ordinal ranking of the experimental thermal conductivities than the calculated thermal conductivity. The Debye temperature is thus a potential descriptor for high-throughput screening of the thermal properties of materials.

cond-mat.mtrl-sci↗

arXiv2014

A RESTful API for exchanging Materials Data in the AFLOWLIB.org consortium

The continued advancement of science depends on shared and reproducible data. In the field of computational materials science and rational materials design this entails the construction of large open databases of materials properties. To this end, an Application Program Interface (API) following REST principles is introduced for the AFLOWLIB.org materials data repositories consortium. AUIDs (Aflowlib Unique IDentifier) and AURLs (Aflowlib Uniform Resource locator) are assigned to the database resources according to a well-defined protocol described herein, which enables the client to access, through appropriate queries, the desired data for post-processing. This introduces a new level of openness into the AFLOWLIB repository, allowing the community to construct high-level work-flows and tools exploiting its rich data set of calculated structural, thermodynamic, and electronic properties. Furthermore, federating these tools would open the door to collaborative investigation of the data by an unprecedented extended community of users to accelerate the advancement of computational materials design and development.

cond-mat.mtrl-sci↗

arXiv2013

Effective and accurate representation of extended Bloch states on finite Hilbert spaces

We present a straightforward, noniterative projection scheme that can represent the electronic ground state of a periodic system on a finite atomic-orbital-like basis, up to a predictable number of electronic states and with controllable accuracy. By co-filtering the projections of plane-wave Bloch states with high-kinetic-energy components, the richness of the finite space and thus the number of exactly-reproduced bands can be selectively increased at a negligible computational cost, an essential requirement for the design of efficient algorithms for electronic structure simulations of realistic material systems and massive high-throughput investigations.

cond-mat.mes-hall↗

arXiv2012

Strain sensitivity and superconducting properties of Nb3Sn from first principles calculations

Using calculations from first principles based on density functional theory we have studied the strain sensitivity of the high-field superconducting magnet A15 Nb3Sn. The Nb3Sn lattice cell was deformed in the same way as observed experimentally on multi-filamentary, technological wires subject to loads applied along their axes. The phonon dispersion curves and electronic band structures along different high-symmetry directions in the Brillouin zone were calculated, at different levels of applied strain, ε, both on the compressive and the tensile side. Starting from the calculated averaged phonon frequencies and electron-phonon coupling, the superconducting characteristic critical temperature of the material, Tc, has been calculated by means of the Allen-Dynes modification of the McMillan formula. As a result, the characteristic bell-shaped Tc vs. ε curve, with a maximum at zero intrinsic strain, and with a slight asymmetry between the tensile and compressive sides, has been obtained. These first-principle calculations thus show that the strain sensitivity of Nb3Sn has a microscopic and intrinsic origin, originating from shifts in the Nb3Sn critical surface. In addition, our computations show that variations of superconducting properties of this compound are correlated to stress-induced changes in both the phononic and electronic properties. Finally, the strain function describing the strain sensitivity of Nb3Sn has been extracted from the computed Tc(ε) curve, and compared to experimental data from multi-filamentary wires. Both curves show the expected bell-shaped behavior, but the strain sensitivity of the wire is enhanced with respect to the theoretical predictions of the bulk, perfectly binary and stoichiometric Nb3Sn. Understanding the origin of this difference might open potential pathways towards the improvement of the strain tolerance in such systems.

cond-mat.supr-con↗

arXiv2007

Ab initio correlation effects on the electronic and transport properties of metal(II)-phthalocyanine based devices

Using first principles calculations in the framework of Density Functional Theory, we investigated the electronic and transport properties of metal(II)-phthalocyanine (M(II)Pc) systems, both in a single molecule configuration and in a model-device geometry. In particular, using the Copper(II)- and Manganese(II)-Pc as prototypical examples, we studied how electronic correlations on the central metal-ion influence the analysis of the electronic structure of the system and we demonstrated that the choice of the exchange-correlation functional, also beyond the standard local or gradient corrected level, is of crucial importance for a correct interpretation of the data. Finally, our electronic transport simulations have shown that M(II)Pc-based devices can act selectively as molecular conductors, as in the case of Copper, or as spin valves, as in the case of Manganese, demonstrating once more the great potential of these systems for molecular nanoelectronics applications.

cond-mat.soft↗

arXiv2005

Band Structure and Quantum Conductance of Nanostructures from Maximally-Localized Wannier Functions: The Case of Functionalized Carbon Nanotubes

We have combined large-scale, $Γ$-point electronic-structure calculations with the maximally-localized Wannier functions approach to calculate efficiently the band structure and the quantum conductance of complex systems containing thousands of atoms while maintaining full first-principles accuracy. We have applied this approach to study covalent functionalizations in metallic single-walled carbon nanotubes. We find that the band structure around the Fermi energy is much less dependent on the chemical nature of the ligands than on the $sp^3$ functionalization pattern disrupting the conjugation network. Common aryl functionalizations are more stable when paired with saturating hydrogens; even when paired, they still act as strong scattering centers that degrade the ballistic conductance of the nanotubes already at low degrees of coverage.

cond-mat.mtrl-sci↗

arXiv2003

Ab-initio transport properties of nanostructures from maximally-localized Wannier functions

We present a comprehensive first-principles study of the ballistic transport properties of low dimensional nanostructures such as linear chains of atoms (Al, C) and carbon nanotubes in presence of defects. A novel approach is introduced where quantum conductance is computed from the combination of accurate plane-wave electronic structure calculations, the evaluation of the corresponding maximally-localized Wannier functions, and the calculation of transport properties by a real-space Green's function method based on the Landauer formalism. This approach is computationally very efficient, can be straightforwardly implemented as a post-processing step in a standard electronic-structure calculation, and allows to directly link the electronic transport properties of a device to the nature of the chemical bonds, providing insight onto the mechanisms that govern electron flow at the nanoscale.

cond-mat.mes-hall↗