Quantum Espresso input file preparation

Dear Beginners,

In this session, I am gonna explain to you the steps to create a simple input file. QE input file must contain six parameters they are ...

• &CONTROL
• &SYSTEM
• &ELECTRONS
• K_POINTS
• ATOMIC_SPECIES
• ATOMIC_POSITIONS

Here the &CONTROL first, we have to define the calculation such as ' scf ' or ' relax '. Next, we have to define the pseudopotential file directory by pesudo_dir. In the example file, we have denoted the pesudo_dir = ' . ' which means that pseudopotentials are on the same directory of the input file. 

input file

In the &SYSTEM, we have to specify the crystal system. Here I downloaded the crystal information file from COD http://www.crystallography.net/cod/search.html. Our CIF file belongs to the cubic system. We have the lattice parameter as A=B=C= 5.46873Å. So we were given a = 5.46873. Then we have to specify The ecutwfc (Kinetic Energy cutoff for wave function). I have given define as 25 Ry. ibrav denotes our bravais lattice index, our crystal system belong to P1(simple cubic). So I choose 1 here; if it is FCC ibrav=2 similarly for other cases, https://www.quantum-espresso.org/Doc/INPUT_PW.html#idm199 (referred from). 

 nat is the total number of atoms in the unitcell.

 ntyp denotes total types of atoms in the unitcell. 

K_POINTS chooses to be automatic. We have a full symmetric system. It will not work for symmetry broken structures. ATOMIC_SPECIES must have the atomic mass and pseudopotential file. ATOMIC_POSITIONS copied from the CIF file, each position should be named by the atomic label. This is the simple input file format for quantum espresso. The file has to be saved in the specified directory as .in format [E-g: Si.in]. Moreover, it should contain the Pseudopotential file (you can download it from Quantum espresso official site).

let's do the calculation  by the following  command

 $ pw < Si.in > Si.out              # and press enter key

▲This will take time to finish, don't close the command prompt until the process to complete. 

Run command

File directory ad CMD after the run command

Check the Si.out file, it can be accessed by the help of Notepad.
 link for pseudopotentials https://www.quantum-espresso.org/pseudopotentials

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                                         JOB DONE.

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