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A Toy Model of Chemical Reaction Networks - TBI - Universität Wien

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14 CHAPTER 3. MOLECULES<br />

Schrödinger equation<br />

ĤΨ = EΨ<br />

⇑<br />

⇓<br />

Born-Oppenheimer<br />

LCAO and Extended Hückel<br />

VSEPR and Tight Binding<br />

Generalized Eigenvalue Problem<br />

⎛<br />

⎞ ⎛<br />

⎞<br />

. .. . ..<br />

⎜<br />

⎟ ⎜<br />

⎟<br />

⎝ H AOi −AO j ⎠C = ⎝ S AOi −AO j ⎠CE<br />

. .. . ..<br />

Figure 3.1: Schematic derivation <strong>of</strong> the used electronic calculation method.<br />

H AOi −AO i<br />

, S AOi −AO j<br />

and K are given parameters (see equations 3.13).<br />

the Schrödinger equation is separated into a part describing the electronic<br />

wave function Ψ el for fixed nuclei,<br />

Ĥ el Ψ el = E el Ψ el , (3.3)<br />

and a part describing the nuclear wave function. The electronic Hamilton<br />

operator is:<br />

(<br />

)<br />

∑e −<br />

Ĥ el = − 1 2 ˆ∇<br />

∑nuc<br />

2 Z I<br />

∑e − ∑e − 1 ∑nuc<br />

∑nuc<br />

Z I Z J<br />

i −<br />

+ , (3.4)<br />

r<br />

i<br />

I iI r<br />

i j>i ij r<br />

} {{ } }{{} I J>I IJ<br />

} {{ }<br />

ĝ ij V n<br />

ĥ i<br />

+<br />

where ˆ∇ is the nabla operator, Z i is the nuclear charge <strong>of</strong> the atom i and r ij

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