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Solid state physics
lectures
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0d599e79
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0d599e79
authored
5 years ago
by
Anton Akhmerov
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!77
Solutions to lecture 5: LCAO model
Pipeline
#29126
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5 years ago
Stage: build
Stage: deploy
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src/5_atoms_and_lcao_solutions.md
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14 additions, 20 deletions
src/5_atoms_and_lcao_solutions.md
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20 deletions
src/5_atoms_and_lcao_solutions.md
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20
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0d599e79
...
...
@@ -20,69 +20,63 @@
1.
$$
\p
si(x) =
\b
egin{cases}
&
\s
qrt{
\k
appa}e^{
\k
appa
(x-x_1)}, x<x_1
\\
&
\s
qrt{
\k
appa}e^{-
\k
appa
(x-x_1)}, x>x_1
&
\s
qrt{
κ}e^{κ
(x-x_1)}, x<x_1
\\
&
\s
qrt{
κ}e^{-κ
(x-x_1)}, x>x_1
\e
nd{cases}
$$
Where $
\k
appa
=
\s
qrt{
\f
rac{-2mE}{
\h
bar
^2}} =
\f
rac{mV_0}{
\h
bar
^2}$.
Where $
κ
=
\s
qrt{
\f
rac{-2mE}{
ħ
^2}} =
\f
rac{mV_0}{
ħ
^2}$.
The energy is given by $
\e
psilon_1 =
\e
psilon
_2 = -
\f
rac{mV_0}{
\h
bar
^2}$
The energy is given by $
ϵ_1 = ϵ
_2 = -
\f
rac{mV_0}{
ħ
^2}$
The wave function of a single delta peak is given by
$$
\p
si_1(x) =
\f
rac{
\s
qrt{mV_0}}{
\h
bar
}e^{-
\f
rac{mV_0}{
\h
bar
^2}|x-x_1|}
\p
si_1(x) =
\f
rac{
\s
qrt{mV_0}}{
ħ
}e^{-
\f
rac{mV_0}{
ħ
^2}|x-x_1|}
$$
$
\p
si_2(x)$ can be found by replacing $x_1$ by $x_2$
2.
$$
H = -
\f
rac{mV_0^2}{
\h
bar
^2}
\b
egin{pmatrix}
1/2+
\e
xp(-
\f
rac{mV_0}{
\h
bar
^2}(x_2-x_1)) &
\e
xp(
\f
rac{mV_0}{
\h
bar
^2}(x_2-x_1))
\\
\e
xp(-
\f
rac{mV_0}{
\h
bar
^2}(x_2-x_1)) &
1/2+
\e
xp(+
\f
rac{mV_0}{
\h
bar
^2}(x_2-x_1))
H = -
\f
rac{mV_0^2}{
ħ
^2}
\b
egin{pmatrix}
1/2+
\e
xp(-
\f
rac{mV_0}{
ħ
^2}(x_2-x_1)) &
\e
xp(
\f
rac{mV_0}{
ħ
^2}(x_2-x_1))
\\
\e
xp(-
\f
rac{mV_0}{
ħ
^2}(x_2-x_1)) &
1/2+
\e
xp(+
\f
rac{mV_0}{
ħ
^2}(x_2-x_1))
\e
nd{pmatrix}
$$
3.
$$
\e
psilon
_{
\p
m} =
\b
eta(3/2+
\c
osh{2
\a
lpha
}+2
\c
osh{
\a
lpha
}
\p
m
\c
osh{
\a
lpha
})
ϵ
_{
\p
m} =
\b
eta(3/2+
\c
osh{2
α
}+2
\c
osh{
α
}
\p
m
\c
osh{
α
})
$$
Where $
\b
eta = -
\f
rac{mV_0^2}{
\h
bar
^2}$ and $
\a
lpha
=
\f
rac{mV_0}{
\h
bar
^2}(x_2-x_1)$
Where $
\b
eta = -
\f
rac{mV_0^2}{
ħ
^2}$ and $
α
=
\f
rac{mV_0}{
ħ
^2}(x_2-x_1)$
### Question 3
1.
$$
H_{
\m
athcal{E}} = eR
E
H_{
\m
athcal{E}} = eR
\m
athcal{E},
$$
Where R is the distance between the negatively charged electrons and the positive charged nuclei.
where R is the distance between the negatively charged electrons and the positive charged nuclei.
2.
$$
H_{eff} =
\b
egin{pmatrix}
E_0 -
\g
amma & -t
\\
-t & E_0 +
\g
amma
\e
nd{pmatrix}
$$
Where $
\g
amma = e d
\m
athcal{E}/2$ and where we have used that $$⟨1|H_{eff}|1⟩ = -e d
\m
athcal{E}/2⟨1|1⟩ = e d
\m
athcal{E}/2$$
3.
The eigenstates of the Hamiltonian are given by:
$$
E_{
\p
m} = E_0
\p
m
\s
qrt{t^2+
\g
amma^2}
$$
The ground state wave function is:
$$
\b
egin{split}
|
\p
si⟩ &=
\f
rac{t}{
\s
qrt{(
\g
amma+
\s
qrt{
\g
amma^2+t^2})^2+t^2}}
\b
egin{pmatrix}
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