Parallel implementation of the ab initio CRYSTAL program: electronic structure calculations for periodic systems

CRYSTAL is an ab initio electronic structure program, based on the linear combination of atomic orbitals, for periodic systems. This paper concerns the ability of CRYSTAL to exploit massively parallel computer hardware. A brief review of the theory, numerical implementations and parallel solutions will be given and some of the functionalities and capabilities highlighted. Some features that are unique to CRYSTAL will be described and development plans outlined.

Enhanced Eu3+ emission in aqueous phosphotungstate colloidal systems: stabilization of polyoxometalate nanostructures

Luminescent Eu(3+)-containing polyphosphate-tungstate aqueous colloidal systems were prepared and studied as a function of the relative polyphosphate-tungstate content. In polyphosphate-rich solutions, Eu(3+) ions occupy cagelike sites composed of phosphate groups from the metaphosphate chains. In these sites, an average number of 0.5 water molecule coordinates to an Eu(3+) ion and the (5)D(0) emission quantum efficiency is 0.22. Tungstate addition leads to important modifications in neighboring Eu(3+) leading to coordination sites in the aqueous medium where metal ions are completely hidden from interactions with solvent molecules. Transmission electron microscopy results clearly show W-rich nanoparticles with sizes between 5 and 10 nm for all tungstate relative concentrations. For high tungstate relative contents (above 30 mol %), spectroscopic results suggest the presence of Eu(3+) in polyoxometalate (POM)-like sites by comparison with the well-known decatungstoeuropate [EuW(10)O(36)](9-) structure. These new aqueous colloids display surprisingly high (5)D(0) emission quantum efficiencies of ca 80% because of the strong ligand field provided by tungstate POM ligands and the complete absence of water molecules from the Eu(3+) first coordination shell.

Case mix at the European Institute of Oncology: first report of the Tumour Registry, 2000-2002

Introduction:

An institutional and centralized hospital-based tumour registry (TR) is the ideal supporting tool for the organization and management of clinical data in a comprehensive cancer centre. The purpose of this paper is to describe the development of the TR at the European Institute of Oncology (IEO), Milan, Italy, from its origin to its current applications.

Material and methods:

After a series of meetings with members of administrative, clinical, research and informatics departments, the TR was activated in March 2006 with the aim of collecting data on all the individuals referred to the institute, with or at risk of developing a tumour. It was implemented on an Oracle™-based interface. A minimum dataset of variables was defined and data collection was divided into four forms, which together gather all the relevant data on patients, tumours, treatments and subsequent events.

Results:

After a six-month pilot period, which involved the training of the tumour registrars, adjustments to the structure of the registry, development of a data quality control procedure and finalization of the operative protocol, since September 2006 the data collection has been fully operative. Five registrars have been chronologically entering data of all individuals who visited the IEO for the first time since 1 January 2000. As of March 2009, data on 69,637 individuals and 43,567 tumours has been reviewed, recoded and registered in the TR. Twenty-two per cent of the tumours (n=9578) were first invasive primaries, diagnosed and treated in the IEO; the most common sites were breast (n=4972), lung (n=627), intestines (n=479) and prostate (n=376).

Conclusion:

The IEO TR has been proven functional and reliable in monitoring the activity of the hospital, allowing extraction of data from any subpopulation with characteristics of interest. The structured and centralized TR represents an important tool for our research-oriented institution.

Vibrational properties of nanometric AB(2) ionic clusters

A broad survey of harmonic dynamics in AB(2) clusters with up to N = 3000 atoms is performed using a simple rigid ion model, with ionic radii selected to give rutile as the ground state structure for the corresponding extended crystal. The vibrational density of states is already close to its bulk counterpart for N∼500, with characteristic differences due to surfaces, edges and vertices. Two methods are proposed and tested to map the cluster vibrational states onto the rutile crystal phonons. The net distinction between infrared (IR) active and Raman active modes that exists for bulk rutile becomes more and more blurred as the cluster size is reduced. It is found that, in general, the higher the IR activity of the mode, the more this is affected by the system size. IR active modes are found to spread over a wide frequency range for the finite clusters. Simple models based on either a crude confinement constraint or surface pressure arguments fail to reproduce the results of the calculations. The effects of the stoichiometry and dielectric properties of the surrounding medium on the vibrational properties of the clusters are also investigated.

Path-integral study of a two-dimensional Lennard-Jones glass

The glass transition in a quantum Lennard-Jones mixture is investigated by constant-volume path-integral simulations. Particles are assumed to be distinguishable, and the strength of quantum effects is varied by changing variant Planck's over 2pi from zero (the classical case) to one (corresponding to a highly quantum-mechanical regime). Quantum delocalization and zero point energy drastically reduce the sensitivity of structural and thermodynamic properties to the glass transition. Nevertheless, the glass transition temperature T(g) can be determined by analyzing the phase space mobility of path-integral centroids. At constant volume, the T(g) of the simulated model increases monotonically with increasing variant Planck's over 2pi. Low temperature tunneling centers are identified, and the quantum versus thermal character of each center is analyzed. The relation between these centers and soft quasilocalized harmonic vibrations is investigated. Periodic minimizations of the potential energy with respect to the positions of the particles are performed to determine the inherent structure of classical and quantum glassy samples. The geometries corresponding to these energy minima are found to be qualitatively similar in all cases. Systematic comparisons for ordered and disordered structures, harmonic and anharmonic dynamics, classical and quantum systems show that disorder, anharmonicity, and quantum effects are closely interlinked.