## The H2 molecule

In this section you will calculate the wavefunction of a H2 molecule by loading a CRYSTAL input file: H2.inp

Exercise 1: Start DLVisualize and run a CRYSTAL calculation:

> Calculate->CRYSTAL->Run SCF Input file
> Click on Browse
> Select H2.inp
> Select OK
> Select OK

The Job List panel will open automatically and look something like this;

Select the job and the status line should report "Job has completed" - like this;

> Click on Recover Files.

A model of H2 should have appeared in the DLV 3DView window.

### Take a moment to familiarise yourself with DLV ...

On main panel the square icons are toggles which control how the 3D structure is displayed. A help message is displayed when you pass the mouse over each button. At first you are in rotate mode and can spin the structure by dragging with the right mouse button. Try changing to scale mode and translate mode etc.

Open the Structure Display panel

> Display->Structure

Try out the controls on this panel - you can change the size of the atoms, display bonds etc etc.

Give the current model a suitable name. This will be used as the label for this model in subsequent CRYSTAL simulations.

> Edit -> Model -> Name
> Change "Model_1" to something suitable; say "H2".

Note:

> For the change to take effect you must press Return.
> You'll see the name of the graphics window change to "DLV 3DView - H2";

In the DLV 3DView window, if the two hydrogen atoms are selected (just left-click on them), the H-H distance will appear in the main window.

A second window will open displaying the output from the CRYSTAL calculation (the LogFile).

It should look something like H2.out

Take some time to read through the output in order to answer to the following questions.

Questions:

1. What is the H-H distance?
   Compare with the reported value in literature.
2. Did you use the same hamiltonian/method adopted in the calculation of the hydrogen atom?
3. What is the energy of the hydrogen molecule in Hartree?
   In the output, the energy is given in atomic unit (Hartree).
   Convert the energy in eV and in J.
   Compare this energy with the exact energy of two isolated hydrogen atoms. Which conclusion can be drawn?
4. What are the energies of the molecular orbital?
   Hints: Look for the string "FINAL EIGENVALUES (A.U.)" at end of the output.
   The energies are given in atomic unit (Hartree). Convert in eV and in J.
5. Plot the bonding and the anti-bonding level energies together with the atomic orbital energy?
6. Calculate the energy gap between HOMO and LUMO?

Optional questions::

1. Compare the calculated energy gap between HOMO and LUMO with the experimental value.

Index Next