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My PhD thesis - Condensed Matter Theory - Imperial College London

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CHAPTER 8. APPLYING THE PLASMON NORMAL MODE THEORY TO<br />

SLAB SYSTEMS<br />

1<br />

0.8<br />

0.6<br />

0.4<br />

0.2<br />

0<br />

0<br />

1<br />

2<br />

3<br />

4<br />

∆r ll 5<br />

6<br />

7<br />

8 -4<br />

-3<br />

-2<br />

-1<br />

0<br />

1<br />

z<br />

2<br />

3<br />

4<br />

Figure 8.7: The fixed electron is at z ′ = 1.0: inside the slab but close to the surface.<br />

the Coulomb interaction is subsumed into Ĥpl; the remaining screened interaction<br />

stays in Ĥsr. The Schrödinger equation has been effectively separated; the groundstate<br />

eigenfunction is then a product of the form<br />

Ψ pr = Ψ pl Ψ sr . (8.102)<br />

The basis for the separation is the physical observation that plasmons exist.<br />

The short-range wave function does not contain information about the longrange<br />

correlations between electrons; however, it should contain the short-range<br />

correlations. The conventional trial wave functions used in QMC have<br />

Ψ sr = D ↑ D ↓ , (8.103)<br />

where the determinants are made up of orbitals obtained from a mean-field calculation.<br />

This wave function does not include the necessary information about short-<br />

144

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