Structural and electronic properties of semiconductors and metals: Difference between revisions
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The use of NAMELISTS allows to specify the value of an input variable only when it is needed and to define default values for most variables that then need not be specified. Variable can be inserted in any order. NAMELISTS are read in a specific order. | The use of NAMELISTS allows to specify the value of an input variable only when it is needed and to define default values for most variables that then need not be specified. Variable can be inserted in any order. NAMELISTS are read in a specific order. | ||
INPUT CARDS are specific of QuantumESPRESSO codes and are used to provide input data that are always needed. | |||
Revision as of 11:50, 1 December 2020
Prev: LabQSM#Lecture 1: Basic DFT calculations and Convergences
Structural and electronic properties of Diamond
In this tutorial we will see how to setup a calculation and to get total energies using the PW code from the Quantum ESPRESSO distribution.
Some helpful conversions:
1 bohr = 1 a.u. (atomic unit) = 0.529177249 angstroms.
1 Rydberg = 13.6056981 eV
1 eV =1.60217733 x 10-19 Joules
For all first-principles calculations, you must pay attention to two convergence parameters. The first one is the energy cutoff, which is the max kinetic energy used in wave-function expansion. The second is the number of k-points, which measures how well the continuous integral over the BZ is discretized.
Diamond is a face-centered cubic structure with two C atoms at 0 0 0 and 0.25 0.25 0.25 a is the lattice parameter
Now let's see in detail how a QE input is structured to make a total energy calculation for this system. An example can be found in ~/LabQSM/LAB_1/test_diamond/scf.diamond.in that you can read e.g. using the editor vi:
&CONTROL
prefix='diamond',
calculation = 'scf'
restart_mode='from_scratch',
pseudo_dir = './pseudo/'
outdir = './SCRATCH'
/
&SYSTEM
ibrav = 2,
celldm(1) = 6.7402778
nat = 2,
ntyp = 1,
ecutwfc = 40.0
/
&ELECTRONS
mixing_mode = 'plain'
mixing_beta = 0.7
conv_thr = 1.0d-8
/
ATOMIC_SPECIES
C 12.011 C.pz-vbc.UPF
ATOMIC_POSITIONS (alat)
C 0.00 0.00 0.00
C 0.25 0.25 0.25
K_POINTS {automatic}
4 4 4 0 0 0
The input file for PWscf is structured in a number of NAMELISTS and INPUT CARDS:
&NAMELIST1 ... / &NAMELIST2 ... / &NAMELIST3 ... / INPUT_CARD1 .... .... INPUT_CARD2 .... ....
The use of NAMELISTS allows to specify the value of an input variable only when it is needed and to define default values for most variables that then need not be specified. Variable can be inserted in any order. NAMELISTS are read in a specific order. INPUT CARDS are specific of QuantumESPRESSO codes and are used to provide input data that are always needed.