B. E. Larson

Modeling Large Surface Reconstructions on the Connection Machine

Using a massively parallel computer, we undertake an ab initio investigation of the Si(111)-(7×7) surface reconstruction. Calculation of the total energy of an ~700 effective atom supercell at an 8 Ry plane wave cutoff allows us to determine (1) the energy difference between the (7×7) and (2×1) reconstructions, (2) the relaxed atomic geometry, (3) the scanning tunneling microscope topographs as a function of bias voltage and (4) the occupied and unoccupied electronic states.

Implementation of the Car–Parrinello algorithm for ab initio total energy calculations on a massively parallel computer

An implementation of the Car–Parrinello algorithm for total energy pseudopotential calculations is undertaken on a massively parallel supercomputer, the Connection Machine CM‐2. Its large memory and throughput makes feasible computations with systems involving more atoms than previously possible on conventional vector supercomputers. Calculations of the Takayanagi 7×7 reconstruction of the Si(111) surface demonstrate that computations involving 1000 atoms at realistic cutoff energies are now possible using ab initio techniques.

Holes in the Quantum Antiferromagnet: The Theory of Small Polarons

The spin-hole coherent states path integral is used to generate a systematic large-spin expansion of the t-J model on the square lattice. The single hole’s classical energy is minimized by small polarons with short ranged interactions. We derive the polarons’ low energy Lagrangian in which inter-sublattice hopping has been eliminated. The polarons’ interaction with the Neel gauge field was argued to produce superconductivity in the magnetically disordered phase. We discuss the relevance of this model to experiments in slightly doped copper oxides.