Hello,
I am a newbie in theoretical solid-state physics. I am now trying to calculate
electronic energy-band structures using Quantum ESPRESSO solver.
The relevant cell (lattice) has following conditions;
1. This unit cell is described by three lattice vectors
1. They are, v1=(-0.5,0.5,0.0), v2=(0,1,-1), v3=(-0.5,0.5,1.0)
1. vectors are normalized with a-lattice length
1. This unit cell has eight-atoms
1. four cations (C) and four anions (A)
1. The system has effective cubic symmetry
Based on these conditions, I wrote a part of input file as below. C and A respectively
stand for cation and anion. I thought that the atoms should be just allotted
on apexes (vertices) of a cube. I wonder this Is correct?
Thanks for any advices. Answers using cif or VASP Poscar formats are also
very welcome so that they can be converted with cif2cell or Vesta.
CELL_PARAMETERS -0.5 0.5 0.0 0.0 1.0 -1.0 0.5 0.5 1.0 ATOMIC_POSITIONS C 0 0 0 C 1 1 0 C 0 1 1 C 1 0 1 A 1 0 0 A 1 1 1 A 0 0 1 A 0 1 0
If you want to use a particular number as the unit cell length, you want to use alat or celldm(1) as part of your definition as you can see here:
https://www.quantum-espresso.org/Doc/INPUT_PW.html
You also want to define your CELL_PARAMETERS as a function of alat then.
As for the atomic positions, it's unclear to me: are you trying to define them as a function of lattice vectors? Then they should be defined as a function of 'crystal'. It's hard to get more specific without knowing what the material you're looking at is. Another way to get a nice input is, if you can get the experimental structure from ICSD for example, or an initial calculated structure from pymatgen (materials project), you can use ASE to convert your structure from .cif file to a quantum espresso input. I am happy to provide a simple script to do so if you need it. The link for ASE is here: https://wiki.fysik.dtu.dk/ase/dev/install.html
Use VESTA software to create your lattice. There is an option of exporting the .cif file as output. This is the output for the QE. If you are looking for new structures this will help.
(or)
If you are looking for old structures/ combinations use materials project website for the same.
Hope this helps.
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