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Two of the most widely used electronic-structure theory methods, namely, Hartree–Fock and Kohn–Sham density functional theory, require the iterative solution of a set of Schrödinger-like equations. The speed of convergence of such a process depends on the complexity of the system under investigation, the self-consistent-field algorithm employed, and the initial guess for the density matrix. An initial density matrix close to the ground-state matrix will effectively allow one to cut out many of the self-consistent steps necessary to achieve convergence. Here, we predict the density matrix of Kohn–Sham density functional theory by constructing a neural network that uses only the atomic positions as information. Such a neural network provides an initial guess for the density matrix far superior to that of any other recipes available. Furthermore, the quality of such a neural-network density matrix is good enough for the evaluation of interatomic forces. This allows us to run accelerated ab initio molecular dynamics with little to no self-consistent steps.

In the reset process of phase-change memories, the active material is brought rapidly above its melting temperature by Joule heating. Atomic migration in the liquid state due to the high electric field can lead to alloy demixing and eventually to device failure. The electromigration force Fresponsible for ionic migration is proportional to the electric field E, via the effective charge Z* (F= eZ*E, where eis electron charge). The determination of Z* is thus of great relevance for the electrothermal modeling of devices. We show that a direct first-principles calculation of the effective charges in metallic liquids is possible by computing the atomic forces in the presence of both an electric field and an electronic current within a nonequilibrium Green’s function method based on density functional theory. We present results on the effective charges for GeTe and Sb2Te3in their liquid state obtained with a calculation including wind forces.

We investigate the effect of quantum confinement on the electronic structure of diluted magnetic semiconductor Ga1-xMnxAs using a combination of tight-binding and density functional methods. We observe half metallic behavior in the clusters as well as a strong majority-spin Mn d−As p hybridization down to sizes as small as 20 Å in diameter. Below this size, the doped holes are significantly self-trapped by the Mn sites, signaling both valence and electronic transitions. Our results imply that magnetically doped III−V nanoparticles will provide a medium for manipulating the electronic structure of dilute magnetic semiconductors while conserving the magnetic properties and even enhancing them in certain size regimes.

We study spin-dependent electronic transport across ferromagnet/superconductor ballistic junctions modeled using tight-binding Hamiltonians with s, p and d orbitals and material-specific parameters. The first result of this paper is that, by accurately modeling the band structure of the bulk materials, one can reproduce the measured differential conductance of Cu/Pb nanocontacts1,2. In contrast the differential conductance of CO/Pb contacts can only be reproduced if an enhanced magnetic moment is present at the interface. The second result concerns the reliability of a method proposed in Refs. 1–3 for determining the degree of polarization of a ferromagnet. By fitting the material-specific differential conductance curves to curves calculated using a single-band model we show that this method does not yield reliable values for polarization and spin-dependent transmission.

CT plays an important role for the pre-surgical evaluation of rectal cancer, both for staging versus RT and for planning the operation. Pelvic scans provide the surgeon with a complete, readable map of the anatomy. The aim of the study is to optimise the protocol for CT of rectal cancer.The luminal distension of visceral wall has been obtained in a clean, well tolerable way by using a balloon catheter filled with water. The catheter is positioned in the rectum at the level of the neoplastic lesion. It consists of a 20cm long latex balloon 6 cm in diameter, assembled over 12F double-way polyethylene catheter: one to inflate the balloon, the second for a guidewire, both for giving stiffness to the system, to advance it and to make the catheter radiopaque to evaluate the correct positioning by CT Fluoroscopy or Scout View. The balloon in gently injected with water, monitoring the degree of distension on minimal discomfort complained by the patient. Optimal distension is usually obtained by injecting 100–200 ml of water. The patient decubit is determined by the position of the lesion leaving it sloping.The scans are performed by a General Electric Pro Speed. After the exam without contrast, 80ml bolus of lopamidol 370 is injected in 60′.CT with the rectal balloon allows a precise evaluation of a series of parameters important for the pre-surgical staging: the distance between anal sphincters and tumor, extension of the tumor and the invasion of perirectal fat and surrounding structures, lymphnodes metastases.The execution of this exam is simple and clean. Rectal distension is well tolerated by patients, without complaints as when entire colon is involved. Avoiding the injection of contrast material in the colon, the CT doesn’t interfere with other exams that can be executed on the same day.The quality of images allows a high diagnostic accuracy.

The visualization of solid, echogenic content within a cystic lesion or a dilated duct poses the diagnostic problem of differentiating debris and clots versus a solid disorder. We used Color Doppler (CD) to asses vascular abnormalities within intracystic and intraductal lesions.Between January and November 1995 we encountered 48 complex cystic lesions and 9 dilated ducts with echogenic material. We used high frequency US probes (10 or 13 MHz) to assess the lesions and we also performed CD with low PRF (500Hz) to detect slow flow.All the patients underwent US guided aspiration biopsy of the complex cistic lesion with the tip of the needle carefully directed within the echogenic portion. In 39 cases the CD was negative as well as the cytological exam. Nine CD-positive cases were associated with 7 papillomas and 2 carcinomas and underwent surgery. Blood flow signal had been detected in 3 of the 4 cases with papilloma, while one was falsely negative. Two small cystic lesions (diameter less than 7mm) showed a clear CD signal, due to an artefactual intralesion projection of a nerby running vessel: the cytology was negative.We think that CD should always be performed in the assesment of intracystic and intraductal solid projections, but a better sensitivity to flow in small blood vessels is still needed.