Showing papers by "José M. Soler published in 1995"

Projection of plane-wave calculations into atomic orbitals

Abstract: The projection of the eigenfunctions obtained in standard plane-wave first-principle electronic-structure calculations into atomic-orbital basis sets is proposed as a formal and practical link between the methods based on plane waves and the ones based on atomic orbitals. Given a candidate atomic basis, ({\it i}) its quality is evaluated by its projection into the plane-wave eigenfunctions, ({\it ii}) it is optimized by maximizing that projection, ({\it iii}) the associated tight-binding Hamiltonian and energy bands are obtained, and ({\it iv}) population analysis is performed in a natural way. The proposed method replaces the traditional trial-and-error procedures of finding appropriate atomic bases and the fitting of bands to obtain tight-binding Hamiltonians. Test calculations of some zincblende semiconductors are presented.

Physical parameters that control the imaging of purple membranes with the scanning tunneling microscope

Abstract: The dominant physical and geometrical parameters for imaging hydrated purple membranes with the scanning tunneling microscope are identified and characterized. These are sample voltage, current density, and tip radius. Purple membranes are imaged with vertical and lateral resolution of 0.7 nm and 15 nm, respectively. We also found that the apparent height of the membranes depends on the tip-substrate separation. These experiments pose the problem of electron transport through 5-10 nm thick insulating materials. We propose a model where the contrast mechanism is controlled by two factors, the electric field at the interface and the transmission through empty states in the membrane.

Mixed Approach to Incorporate Self-Consistency into Order-N LCAO Methods

Abstract: We present a method for selfconsistent Density Functional Theory calculations in which the effort required is proportional to the size of the system, thus allowing the aplication to problems with a very large size. The method is based on the LCAO approximation, and uses a mixed approach to obtain the Hamiltonian integrals between atomic orbitals with Order-N effort. We show the performance and the convergence properties of the method in several silicon and carbon systems, and in a DNA periodic chain.