Chem 481L
Fall 2009
Lab Module #3
Introduction to Spartan
Due Date:
Noon, Tuesday, September 22
Submit via Blackboard
Goal:
The goal of this week’s module is to learn to use Spartan PC.
Specifically, we build
simple molecules in Spartan and compare the physical properties as calculated by three
different numerical methods.
We will also conduct a study of the equilibrium geometry of a
series of simple alkanes, as described by the same three methods, to ascertain the relationship
between number of basis functions and CPU time.
Research questions:
How does choice of basis set and numerical method inform
calculations? How does CPU time for a calculation depend on basis set?
Readings:
The following chapters in Spartan’s online manual:
Basic Operations; Theoretical
Models; and Choosing Theoretical Models; Common Terms and Acronyms; Units.
Found using
Help button in Spartan Student or at
http://www.wavefun.com/products/windows/StudentPChem/SpPhysChemBook.pdf
Introduction:
A basis set is a collection of functions that, when combined in a linear fashion with appropriate
weighting coefficients, describes a system of interest.
One can choose any collection of
functions with the assurance, from the variational theorem, that the resulting energy will always
be greater than or equal to the true energy of the system.
However, to simplify the already
complex calculations, one usually chooses smartly: a set of basis functions that are real and
normalized; for instance, reduces the time required to perform necessary calculations.
In Lab 2, we used a
minimal basis set
to form molecular orbitals to describe the energy of the
H
2
+ molecule ion.
The molecular orbitals (MOs) were formed from the linear combination of
atomic orbitals (LCAO) that comprised the basis set, which was simply two hydrogenic atomic
orbitals, one centered on each hydrogen nucleus.
One consequence of this minimal basis set
was that the resulting energies, while qualitatively informative, were quantitatively incorrect.
In computational chemistry, one can also choose whether to run
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 Spring '07
 PIELAK
 Atom, Mole, pH, Molecule, Computational chemistry, CPU time, basis functions

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