arXiv subjects

Sohrab Ismail-Beigi

Publications and source records attributed to Sohrab Ismail-Beigi.

58 records · Page 4Linked to original sources

arXiv1999

Ab Initio Study of Screw Dislocations in Mo and Ta: A new picture of plasticity in bcc transition metals

We report the first ab initio density-functional study of <111> screw dislocations cores in the bcc transition metals Mo and Ta. Our results suggest a new picture of bcc plasticity with symmetric and compact dislocation cores, contrary to the presently accepted picture based on continuum and interatomic potentials. Core energy scales in this new picture are in much better agreement with the Peierls energy barriers to dislocation motion suggested by experiments.

cond-mat.mtrl-sci↗

arXiv1999

On the Locality of Physics in Metals, Semiconductors, and Insulators

We present an analytical study of the spatial decay rate $γ$ of the one-particle density matrix $ρ(\vec r,\vec r')\sim\exp(-γ|\vec r-\vec r'|)$ for systems described by single particle orbitals in periodic potentials in arbitrary dimensions. This decay reflects electronic locality in condensed matter systems and is also crucial for O(N) density functional methods. We find that $γ$ behaves contrary to the conventional wisdom that generically $γ\propto\sqrtΔ$ in insulators and $γ\propto\sqrt{T}$ in metals, where $Δ$ is the direct band gap and $T$ the temperature. Rather, in semiconductors $γ\proptoΔ$, and in metals at low temperature $γ\propto T$.

cond-mat.mtrl-sci↗

arXiv1998

Edge-driven transition in surface structure of nanoscale silicon

We present an ab initio exploration of the phenomena which will become important for freestanding structures of silicon as they are realized on the nanoscale. We find that not only surface but also edge effects are important considerations in structures of dimensions on the order of 3 nm. Specifically, for long nanoscale silicon bars, we find two competing low-energy reconstructions with a transition from one to the other as the cross section of the bar decreases. We predict that this size-dependent phase transition has a signature in the electronic structure of the bar but little effect on elastic properties.

cond-mat.mtrl-sci↗

arXiv1998

Paramagnetic structure for the soliton of the $30^\circ$ partial dislocation in silicon

Based on ab initio calculation, we propose a new structure for the fundamental excitation of the reconstructed 30$^\circ$ partial dislocation in silicon. This soliton has a rare structure involving a five-fold coordinated atom near the dislocation core. The unique electronic structure of this defect is consistent with the electron spin resonance signature of the hitherto enigmatic thermally stable R center of plastically deformed silicon. This identification suggests the possibility of an experimental determination of the density of solitons, a key defect in understanding the plastic flow of the material.

cond-mat.mtrl-sci↗