Showing papers by "Roberto Car published in 2000"

First-principles molecular-dynamics study of the (0001) alpha-quartz surface

Abstract: We present an ab initio investigation of the structural and electronic properties of the (0001) alpha-quartz surface. Five different models of this surface are generated by cleavage of the bulk followed by atomic relaxation and constant-temperature molecular dynamics. The most favorable reconstruction presents an unexpected densification of the two uppermost layers of SiO2 tetrahedral units, with three-membered and six-membered rings that do not exist in bulk alpha-quartz. The electronic density of states for this surface is very similar to the bulk one, except for a typical feature of SiO2 under pressure, namely the disappearance of the gap between Si-O bonding and O 2p nonbonding states.

Dangling bond defects at Si-SiO2 interfaces: Atomic structure of the P-b1 center

Abstract: Using a first-principles approach, we characterize dangling bond defects at Si-SiO2 interfaces by calculating hyperfine parameters for several relaxed structures; Interface models, in which defect Si atoms remain close to crystalline sites of the substrate upon relaxation, successfully describe P-b and P-b0 defects at (111) and (100) interfaces, respectively. On the basis of calculated hyperfine parameters, we discard models of the P-b1 defect containing a first neighbor shell with an O atom or a strained bond. A novel model consisting of an asymmetrically oxidized dimer yields hyperfine parameters in excellent agreement with experiment and is proposed as the structure of the P-b1 center.