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fall 09 lm _3 intro spartan

# fall 09 lm _3 intro spartan - Chem 481L Lab Module#3 Due...

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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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fall 09 lm _3 intro spartan - Chem 481L Lab Module#3 Due...

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