Edit3: HemanthHaridas' answer explained why BURAI gave me the result. However, when I opened the same output file using XCrySDen, I got a completely different result (the correct one). So, even though I accepted the answer, I am opening this question again. Since XCrySDen is maintained in a more regular manner than BURAI, I trust the result of XCrySDen cannot understand the discrepancy between XCrySDen result and BURAI result (or alternatively, the result obtained using @HemanthHaridas' explanation).
I was following a youtube tutorial for finding the lattice constant of Si crystal: Project: 3.1 Si crystal constant and density | Quantum Espresso Tutorial 2019. The input file I used is the following:
&control
calculation = 'vc-relax'
prefix = 'si'
etot_conv_thr = 1e-5
forc_conv_thr = 1e-4
/
&system
ibrav=2
celldm(1) =14
nat=2
ntyp=1
ecutwfc=30
/
&electrons
conv_thr=1e-7
/
&ions
/
&cell
cell_dofree='all'
/
ATOMIC_SPECIES
Si 28.0855 Si.pbe-n-rrkjus_psl.1.0.0.UPF
ATOMIC_POSITIONS (alat)
Si 0.00 0.00 0.00 0 0 0
Si 0.25 0.25 0.25 0 0 0
K_POINTS (automatic)
4 4 4 0 0 0
When I run this, I got the output file which gave me the (almost) correct value for the lattice constant of the Si which I found from the output/log file (5.48 Å). However, inside BURAI GUI, there is a window to view the convergence for geometric convergence which indicates a wrong result as can be seen from the image below.
My question is why is the lattice constant converging to a different (wrong) value in the graph, while the output file gives the correct lattice constant (within an error of 1%) after the end of the SCF iteration?
Edit1: The output file espresso.log.opt can be found here. The cell parameters in each step and the volume can be found inside denoted by CELL_PARAMETERS
and new unit-cell volume
, respectively. To find the cell parameter in Bohr radius, I first divided the cell parameter by 0.5 and then multiplied by alat=14. To convert it to Å, one needs to multiply the Bohr radius by 0.529
Edit2: alat multiplier and the x, y and z axes lengths at each step
13.999998 0.696568 0.696568 0.696568
13.999998 0.680759 0.680759 0.680759
13.999998 0.657046 0.657046 0.657046
13.999998 0.644397 0.644397 0.644397
13.999998 0.625422 0.625422 0.625422
13.999998 0.611748 0.611748 0.611748
13.999998 0.591238 0.591238 0.591238
13.999998 0.560472 0.560472 0.560472
13.999998 0.514324 0.514324 0.514324
13.999998 0.526698 0.526698 0.526698
13.999998 0.523420 0.523420 0.523420
13.999998 0.523121 0.523121 0.523121
13.999998 0.523121 0.523121 0.523121
code
blocks, please put the output file there. If it doesn't fit, then you can create a folder called 10324 here and put the file in there. 10324 is the number in this question's URL. $\endgroup$