Systematically convergent method for accurate total energy calculations with localized atomic orbitals

We introduce a method for solving a self consistent electronic calculation within localized atomic orbitals, that allows us to converge to the complete basis set (CBS) limit in a stable, controlled, and systematic way. We compare our results with the ones obtained with a standard quantum chemistry package for the simple benzene molecule. We find perfect agreement for small basis set and show that, within our scheme, it is possible to work with a very large basis in an efficient and stable way. Therefore we can avoid to introduce any extrapolation to reach the CBS limit. In our study we have also carried out variational Monte Carlo (VMC) and lattice regularized diffusion Monte Carlo (LRDMC) with a standard many-body wave function (WF) defined by the product of a Slater determinant and a Jastrow factor. Once the Jastrow factor is optimized by keeping fixed the Slater determinant provided by our new scheme, we obtain a very good description of the atomization energy of the benzene molecule only when the basis of atomic orbitals is large enough and close to the CBS limit, yielding the lowest variational energies.Comment: 22 pages, 6 figures, accepted in Physical Review

Large-scale computing with Quantum ESPRESSO

This paper gives a short introduction to Quantum ESPRESSO: a distribution of software for atomistic simulations in condensed-matter physics, chemical physics, materials science, and to its usage in large-scale parallel computing

Large-scale computing with Quantum ESPRESSO

This paper gives a short introduction to Quantum ESPRESSO: a distribution of software for atomistic simulations in condensed-matter physics, chemical physics, materials science, and to its usage in large-scale parallel computing

The Crossover between Liquid and Solid Electron Phases in Quantum Dots: A Large-Scale Configuration-Interaction Study

We study the crossover between liquid and solid electron phases in a two-dimensional harmonic trap as the density is progressively diluted. We infer the formation of geometrically ordered phases from charge distributions and pair correlation functions obtained via a large scale configuration interaction calculation.Comment: LaTeX 2e, Elsevier style. Four pages, two b/w postscript figures. Submitted to Computer Physics Communications as a proceeding of Conference on Computational Physics, Genova 200

The role of bone metastases on the mechanical competence of human vertebrae

Spine is the most common site for bone metastases. The evaluation of the mechanical competence and failure location in metastatic vertebrae is a biomechanical and clinical challenge. Little is known about the failure behaviour of vertebrae with metastatic lesions. The aim of this study was to use combined micro-Computed Tomography (microCT) and time-lapsed mechanical testing to reveal the failure location in metastatic vertebrae. Fifteen spine segments, each including a metastatic and a radiologically healthy vertebra, were tested in compression up to failure within a microCT. Volumetric strains were measured using Digital Volume Correlation. The images of undeformed and deformed specimens were overlapped to identify the failure location. Vertebrae with lytic metastases experienced the largest average compressive strains (median & PLUSMN; standard deviation: -8506 & PLUSMN; 4748microstrain), followed by the vertebrae with mixed metastases (-7035 & PLUSMN; 15605microstrain), the radiologically healthy vertebrae (-5743 & PLUSMN; 5697microstrain), and the vertebrae with blastic metastases (-3150 & PLUSMN; 4641microstrain). Strain peaks were localised within and nearby the lytic lesions or around the blastic tissue. Failure between the endplate and the metastasis was identified in vertebrae with lytic metastases, whereas failure localised around the metastasis in vertebrae with blastic lesions. This study showed for the first time the role of metastases on the vertebral internal deformations. While lytic lesions lead to failure of the metastatic vertebra, vertebrae with blastic metastases are more likely to induce failure in the adjacent vertebrae. Nevertheless, every metastatic lesion affects the vertebral deformation differently, making it essential to assess how the lesion affects the bone microstructure. These results suggest that the properties of the lesion (type, size, location within the vertebral body) should be considered when developing clinical tools to predict the risk of fracture in patients with metastatic lesions

European actions for High-Performance Computing: PRACE, DEISA and HPC-Europa

Between e-Infrastructures, ESFRI has identified in FP7 High- Performance Computing a strategic priority for Europe. In order to have the highest return from the associated massive economical and political commitment, HPC resources must be exploited at the highest level. Their access must be effective and capillary, their services must allow more and more people to use the resources, regardless their geographical location. Projects like PRACE, DEISA and HPC-Europa have been supported by the EU to cope with such issues providing the best solutions for the European research community

Optimizing topology for quantum probing with discrete-time quantum walks

Discrete-time quantum walk (DTQW) represents a convenient mathematical framework for describing the motion of a particle on a discrete set of positions when this motion is conditioned by the values of certain internal degrees of freedom, which are usually referred to as the {\em coin} of the particle. As such, and owing to the inherent dependence of the position distribution on the coin degrees of freedom, DTQWs naturally emerge as promising candidates for quantum metrology. In this paper, we explore the use of DTQWs as quantum probes in scenarios where the parameter of interest is encoded in the internal degree of freedom of the walker, and investigate the role of the topology of the walker's space on the attainable precision. In particular, we start considering the encoding of the parameter by rotations for a walker on the line, and evaluate the quantum Fisher information (QFI) and the position Fisher information (FI), explicitly determining the optimal initial state in position space that maximizes the QFI across all encoding schemes. This allows us to understand the role of interference in the position space and to introduce an optimal topology, which maximizes the QFI of the coin parameter and makes the position FI equal to the QFI.Comment: 11 pages, 5 figure

In vitro characterization of the three-dimensional strain pattern in human vertebrae affected by metastases

La colonna vertebrale è la principale sede di metastasi, le quali possono alterare la normale distribuzione dei tessuti ossei e ridurre la capacità della vertebra di sostenere carichi. L’instabilità spinale causata dalle metastasi, tuttavia, è di difficile determinazione. La caratterizzazione meccanica delle vertebre metastatiche permetterebbe di identificare e, di conseguenza trattare, quelle ad alto rischio di frattura. In questo studio, ho valutato il comportamento meccanico a rottura di vertebre umane affette da metastasi misurando in vitro il campo di deformazione. Undici provini, costituiti da due vertebre centrali, una metastatica e una sana, sono stati preparati e scansionati applicando carichi graduali di compressione in una micro-tomografia computerizzata (μCT). Le deformazioni principali sono state misurate attraverso un algoritmo globale di Digital Volume Correlation (DVC) e successivamente sono state analizzate. Lo studio ha rivelato che le vertebre con metastasi litiche raggiungono deformazioni maggiori delle vertebre sane. Invece, le metastasi miste non assicurano un comportamento univoco in quanto combinano gli effetti antagonisti delle lesioni litiche e blastiche. Dunque la valutazione è stata estesa a possibili correlazioni tra il campo di deformazione e la microstruttura della vertebra. L'analisi ha identificato le regioni in cui parte la frattura (a più alta deformazione), senza identificare, in termini microstrutturali, una zona preferenziale di rottura a priori. Infatti, alcune zone con un pattern trabecolare denso, presunte più rigide, hanno mostrato deformazioni maggiori di quelle dei tessuti sani, sottolineando l’importanza della valutazione della qualità del tessuto osseo. Questi risultati, generalizzati su un campione più ampio, potrebbero essere utilizzati per implementare nuovi criteri negli attuali sistemi di valutazione dell'instabilità spinale