What does LCAO stand for, and why is it used in computational chemistry? (Note:
ID: 997698 • Letter: W
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What does LCAO stand for, and why is it used in computational chemistry? (Note: the Wikipedia entry on this topic borders on gibberish and should not be consulted for an answer) State the reason why the Hartree-Fock equations for poly-atomic molecules are solved via basis set expansions for the orbitals What is the reason for using 'split-valence, 'triple- 'quadruple-^', ate. basis sets in molecular calculations? Would it be possible to perform an accurate calculation of the H_2 molecule by placing basis functions only on one of the hydrogen? Give reasons for your answer. What is a 'minimal basis' ? Explain why an MO calculation for H2, say, should not use only 1s basis functions but also 2p, 3d, etc. What is the difference between STO and GTO basis functions? Why do we typically need many more GTO functions than STOs for calculations of similar accuracy?Explanation / Answer
a)
LCAO stands for Leniar Combination of Atomic Orbitals.
Computational Chemistry: A mathematical method that is sufficiently well developed that it can be automated for implementation on a computer.
Application of quantum mechanics to computational chemistry by outlining the development of quantum mechanics up to the Schrodinger equation and then show how the equation lead to the simple Huckel method, from which the extended Huckel method. The simple Huckel method starts with the Schrodinger equation in the form H = E. By expressing as a linear combination of atomic orbitals and minimizing E with respect to the LCAO coefficients, we will get a set of simultaneous equation, the secular equations. These are equivalent to single matrix equation.
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