INSTRUCTIONS FOR DAY 1, EXERCISE 4

In this exercise, we will use PWSCF to obtain the equilibrium structure of some simple crystals

Silicon

• Enter the directory ex4. Copy the silicon input file and pseudopotential from example 1
• Edit the input file to perform a variable-cell geometry optimisation by setting calculation='vc-relax'.
• Add the following IONS and CELL name lists (after ELECTRONS)

&ions
upscale =100
/
&cell
Press = 0.0
/

• Press is the target pressure in KBar (1KBar = 0.1 GPa)
• Run the geometry optimisation
• Examine the output file - how does the lattice constant compare to experiment. Note that the forces on the ions are zero due to symmetry.
• Repeat the calculation at a higher pressure

Arsenic

• Run the geometry optimisation for As at zero pressure (As0.bfgs.in is provided)
• Repeat the calculation at 40GPa - what do you observe? Look at the output with Xcrysden. It may help to glance at Physical Review B 78, 174101 (2008) doi:10.1103/PhysRevB.78.174101