VBTutorial1

<< Return to the program

How to modify this page :

• first : log in (top right of this page) ;
• click on [edit] (far right) to edit a section of the page ;
• write your text directly in the wiki page, and click on the "Save page" button (bottom left) to save your modifications

Pictures : how to insert a picture in your text

See also this page for an introduction to the basics of the wiki syntax

Basics of VB theory and XMVB program

To the Tutors

Sason remarks and prospective 2 hours talk +

Philippe's remark on the initially proposed tutorial. are included in bold.

Qualitative

• Exercices from The Book ... >PCH< (30')

Computational

• FH (2 structures), F2 : VBSCF, different correlation wave functions (BOVB, VBCI,...), computation of weights and "charge-shift" character, also compare to CASSCF wave functions in the same basis set (probably to provide in order to avoid to spend time there).
• R-X bond dissociation to R. .X and R(+) (-)X for stable ionic dissociation ... via solvent effects? (is that possible with xiamen ?)

Exercices

Exercise 1 (paper exercise) : The lone pairs of H2O

This exercise aims at comparing two descriptions of the lone pairs of H2O : (i) the MO description in terms of non-equivalent canonical MOs and (ii) the « rabbit-ear » VB description in terms of two equivalent hybrid orbitals.

<math>\Psi_{MO}</math>   <math>\Psi_{VB}</math>

1. Focusing on the lone pairs only, write the four-electron single-determinants MO and VB.
2. Expand VB into elementary determinants containing only n and p orbitals, eliminate determinants having two identical spinorbitals, and show the equivalence between VB and MO.
3. We now remove one electron from H2O. Write the two possible VB structures 1 and 2 in the VB framework.
4. The two ionized states are the symmetry-adapted combinations and . From the sign of the hamiltonian matrix element , give the energy ordering of the two ionized states.
5. By expanding the two ionized states into elementary determinants (dropping the normalization constants), show that they are equivalent, respectively, to the MO configurations and .

Appendix

Hamiltonian matrix element between determinants differing by one spin-orbital :

>> Answer

Exercice 2 : Simple diatomics molecules

Subject

First contact with XMVB on simple diatomics. Examination of the effect of correlation on weights, and bond energies. Calculation of a pure covalent state and (charge-shift) resonance energy.

To do

• Compute of H2 at the VBSCF level.
• Compute HF at the VBSCF, VBCI, and D-BOVB levels. Compute bond energy. Compute a single covalent structure, and deduce the charge-shift resonance energy.
• Same question for F2

Access to files :

title title

Exercice 3 : Dissociation of C(Me)3-Cl

Subject

First calculation beyond diatomics (fragment C(Me)3 and Cl). VB(PCM) method.

To do

• Compute of C(Me)3-Cl at equilibrium distance at the VBSCF and D-BOVB levels.
• Compute C(Me)3-Cl at large inter fragment distance (5Å ?), at the D-BOVB level.
• Redo previous questions using the VB(PCM) option.

Access to files :

title title