Extended Hiickel theory advantage

Key words Extended Hiickel theory, advantages and disadvantages - Structure-property correlation -Extended Hiickel theory, history and impact -Roald Hoffmann... 

In the previous two sections we have discussed the semiempirical extended Hiickel theory and the SCF-Xa-SW method. We have detailed the advantages and disadvantages of these methods for surface structure determination. 

More sophisticated procedures involve taking the start MO coefficients from a semi-empirical calculation, such as Extended Hiickel Theory (EHT) or Intermediate Neglect aif Differential Overlap (TNDO) (Sections 3.12 and 3.9). The EHT method has the advantage that it is readfiy parameterized for allEIements, and irxau provide starF orbitals for systems involving elements from essentially the whole periodic table. An INDO calculation normally provides better start orbitals, but at a price. The EMDO... 

We now turn our attention to a method of deriving molecular orbitals that does not require evaluation of two-electron integrals. This is the method used with the approximate techniques known as extended Hiickel and Hiickel theory. It is also used in perturbational molecular orbital theory, which we present later in this chapter. This method takes advantage of secular determinants, a way in which to represent the Schrbdinger equation as a di-agonalizable matrix. 

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