Jeremy W. Nicklas

Accurate ab initio predictions of III–V direct-indirect band gap crossovers

We report the compositional dependence of the electronic band structure for a range of III–V alloys. Standard density functional theory is insufficient to mimic the electronic gap energies at different symmetry points of the Brillouin zone. The Heyd–Scuseria–Ernzerhof hybrid functional with screened exchange accurately reproduces the experimental band gaps and, more importantly, the alloy concentration of the direct-indirect gap crossovers for the III–V alloys studied here: AlGaAs, InAlAs, AlInP, InGaP, and GaAsP.

Band offsets of semiconductor heterostructures: A hybrid density functional study

We demonstrate the accuracy of the Heyd–Scuseria–Ernzerhof (HSE06) hybrid functional for computing the band offsets of semiconductor alloy heterostructures. The highlight of this study is the computation of conduction band offsets with a reliability that has eluded standard density functional theory. A special quasirandom structure models an infinite random pseudobinary alloy for constructing heterostructures along the (001) growth direction. Our results for a variety of heterostructures establish HSE06’s relevance to band engineering of high-performance electrical and optoelectronic devices.

Magnetic properties of Fe chains on Cu2N/Cu(100): A density functional theory study

We present a density functional study of the magnetic properties of Fe adatoms on Cu2N/Cu(100) surface. The magnetic anisotropy energies of a single Fe atom are in excellent agreement with the available experiments. Our results for the spin densities and exchange coupling strengths for Fe dimer and trimer establish antiferromagnetic configuration to be the ground state due to predominant superexchange interaction mediated by nitrogen atoms in this system.

Ab initio based empirical potential applied to tungsten at high pressure

Density-functional theory forces, stresses and energies comprise a database from which the optimal parameters of a spline-based empirical potential combining Stillinger-Weber and modified embeddedatom forms are determined. Accuracy of the potential is demonstrated by predictions of ideal shear, stacking fault, vacancy migration, elastic constants and phonons all between 0 and 100 GPa. Consistency with existing models and experiments is demonstrated by application to screw dislocation core structure and deformation twinning in a tungsten nanorod. Lastly, the potential is used to study the high-pressure bcc to fcc phase transition.