The core of one part of this program is the
introduction of undergraduates to the world of electronic structure
calculations as a tool in studying the physical properties of molecules
and solids. The 10-week program will begin with a two-week intensive
introduction to molecular orbital (MO) and energy-band calculations
using a user-friendly package (BICON-CEDiT) developed by the Calzaferri
group at the University of Berne based in part on programs developed by
the Hoffmann group at Cornell. This package is based on extended Huckel
theory (EHT) and is strongly intuitive yet, because of its semiempirical
basis, capable of sufficient accuracy to correctly predict material
properties of a very wide range of molecular and solid-state systems.
The introductory material will survey some of the quantum mechanics
behind each program but only to the extent needed to establish the
terminology used in some of the program input. Since the EHT is largely
based on concepts that students with an introductory chemistry
background can readily grasp (atomic ionization energies, orbital
overlap, etc.), the mode of instruction will be heavily oriented towards
visual presentations and tutorial calculations on simple molecules and
solids. 1 week of library research and definition of a problem within
the student's capability will follow the introduction. The next 4-5
weeks would be devoted to carrying through with necessary computation to
solve the problem. The last 2 weeks will be spent on organizing the
results for presentation in American Physical Society style before other
students and faculty. The use of standardized codes has the advantage in
giving the student experience greater portability. Furthermore because
EHT is a widely used approximation the student will be able to recognize
other work in the literature carried out using such codes. Because of
the simplicity of the EHT program, it has tremendous flexibility in
dealing with systems ranging from molecules, to clusters, to solids, and
even to surface/interface systems. Some project areas are: 1) Effect of
ligands on vibrational spectra, spin resonance parameters, optical and
nonlinear optical properties, etc. Each of the perturbations may be
visualized in terms of local-orbital modifications. 2) Electronic and
vibronic features of BCS superconductors such as LiBC and MgB2. Solid
state features such as band-width, band gap, effective mass, density of
states, etc. may be studied, again with emphasis on visual presentation
over detailed theoretical treatment. For a student who is more inclined
toward software development, a project will involve the development of a
tool which uses the output from the EHT code to produce derived
quantities such as electrical conductivity, bulk modulus, phonon
spectra, etc.
The second program deals with the computer simulation of the MPCVD
process. This problem subdivides along two research lines. The first
deals with the chemical kinetics of the gas phase and the heterogeneous
gas/surface reactions. For this the student will learn to use a standard
package (CHEMKIN) and to modify existing model reaction networks to
study the effects of key parameters like temperature, pressure, feed-gas
composition and substrate on the growth of diamond or graphite. The
second line of research is the investigation of the coupling of the
microwave energy and its role in 1) promotion of atomic hydrogen
production and 2) heating of the gas and substrate. For this we will use
a program called ARGUS, which was developed in part for such
applications. The goal is to eventually couple both lines of research
into a package that more fully treats the overall MPCVD process. REU
students Steven Baker, Richard Lee, Brian Geislinger, Danny Green,
MaQuita Warren and Will Shanks have worked on similar computational
materials research projects and made several presentations at the
Alabama Materials Research Conferences [17-18]. |
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