## The H2 polymer

In this section you will calculate the wavefunction and the band structure for the hydrogen polymer with 2 atoms in the periodic cell, H2.
When the cell is doubled, a'=2 a, the cell in the reciprocal space becomes half: a*'= a*/2 .
The energy states that were in the range between a*/4 and X=a*/2 in the band structure obtained at the end of Exercise 2 for the H polymer are now folded back.

Exercise 1: Start DLVisualize, run a CRYSTAL calculation for the H2 polymer: H2_polymer.inp

Exercise 2: Run a CRYSTAL properties calculation of the band structure for the H2 polymer, as explained in Exercise 2 for the H polymer.

In the CRYSTAL Bands panel, type the coordinates of the points (note that the coordinates are expressed in unit of a*'):

Questions:

1. How many bands are visualised in the band structure?
2. What are the differences between the current band structure and the one obtained for the H polymer?
3. Draw the bonding and the anti-bonding combination for each band.

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