confronto VB-MO

Question 1

What is the relationship between the MO and VB methods?

Answer 1

The MO and VB methods become equivalent when the MO method is corrected for electron correlation through configuration interaction and the VB method is corrected for excessive electron correlation by introducing ionic structures.

Question 2

What is the issue with the VB method?

Answer 2

The issue with the VB method is that it suffers from excessive electron correlation.

Question 3

What is the VB method?

Answer 3

The VB method describes electrons using valence bond orbitals that are localized on individual atoms and the molecular function is a linear combination of valence bond structures.

Question 4

What is the issue with the MO method in its current form?

Answer 4

The issue with the MO method in its current form is that the electrons are not sufficiently correlated.

Question 5

What is the issue with the MO method in its current form?

Answer 5

The common approximation used in the MO method is to express molecular orbitals as combinations of atomic orbitals.

Question 6

Come si corregge la correlazione elettronica nel metodo del MO

Answer 6

Considerare una combinazione di due determinanti di Slater. La presenza di una costante permette di ridurre il contributo ionico

Question 7

Describe the Hamiltonian in the MO method

Answer 7

The Hamiltonian in the MO method is written as a sum of the Hamiltonians of each electron in the molecule, which is similar to the hydrogen ion molecule plus an electron-electron repulsion term.

Question 8

What is the function of the molecular orbital in the MO method?

Answer 8

The function of the molecular orbital in the MO method is to choose a configuration (σg1s)(σg1s) and for molecular orbitals, we choose combinations of atomic orbitals.

Question 9

Describe the Hamiltonian in the VB method

Answer 9

The Hamiltonian in the VB method is seen as a sum of two Hamiltonians of the hydrogen atom plus a perturbation term.

Question 10

What is the unperturbed function in the VB method?

Answer 10

The unperturbed function in the VB method corresponds to the two configurations H·1a H·2b ϕa(1)ϕb(2) = f1 and H·2a H·1b ϕa(2)ϕb(1) = f2.

Question 11

a cosa corrisponde la funzione non perturbata nel metodo VB

Answer 11

The unperturbed function in the VB method corresponds to the two configurations H·1a H·2b ϕa(1)ϕb(2) = f1 and H·2a H·1b ϕa(2)ϕb(1) = f2.

Question 12

How do we calculate the probability of finding an electron in a given volume without considering its spin?

Answer 12

We integrate over the coordinates of all other electrons except the one we are interested in.

Question 13

Come si calcola la densità elettronica totale?

Answer 13

The general definition of the likelihood of finding any electron in a volume element in a molecule is given by (xyz) = (∑s1∑s2· ·∫∫· · | |2 dv2dv . .dvn) dv1.

Question 14

What is the difference between the electronic density in the hydrogen molecule using the VB method and the MO method?

Answer 14

The difference between the electronic density in the hydrogen molecule using the VB method and the MO method is given by 0 < Μ O - V B < 2.

Question 15

What is the expression for the electronic density in the hydrogen molecule at the center of the bond using the MO method?

Answer 15

The expression for the electronic density in the hydrogen molecule at the center of the bond using the MO method is (|1Sa^2|^2)22/(1 + Sab)

Question 16

What is the significance of the result obtained from comparing the electronic density in the hydrogen molecule using the VB method and the MO method?

Answer 16

The result obtained from comparing the electronic density in the hydrogen molecule using the VB method and the MO method shows that the MO da una maggiore densita elettronica come ci si poteva
aspettare dal fatto che soottostima la correlazione elettronica. Il metodo VB,
a questo livello di approssimazione, d`a una migliore energia elettronica

Question 17

Describe the probability of finding electrons in a molecule with spin variables

Answer 17

The probability of finding electrons in a molecule with spin variables can be represented by the quantity |Ψ |2 dv1 dv . . dvn, which represents the probability of finding electron 1 in the volume element dv1 with spin s1, electron 2 in volume element dv2 with spin s2, etc.

Question 18

What is the expression for the electronic density in the hydrogen molecule at the center of the bond using the VB method?

Answer 18

ρVB =(1 + Sab) |1sa|^2 *2/(1 + S^2ab)