Good evening, This is my first solid-state electronic structure calculation; please forgive if my questions are obvious. I am not confident in the proper symmetry representation of my system. I attach my input file and associated questions. Don't worry on my value of ecutwfc; I am trying to do cheap calculations at the moment for pedagogy, and do not care how quality a value this is right now. Same goes for my k space points.
&CONTROL calculation = "vd-relax" outdir='/p/work1/workspace/molt/Espresso_Test', pseudo_dir = '/p/home/molt/Espresso_PP', restart_mode = "from_scratch" / &SYSTEM celldm(1) = 1.3454e+01 ecutwfc = 4.00000e+01 ibrav = 2 nat = 74 nspin = 1 ntyp = 2 / &ELECTRONS diagonalization = "david" electron_maxstep = 100 mixing_beta = 7.00000e-01 mixing_mode = "plain" startingpot = "atomic" startingwfc = "atomic+random" / &IONS / &CELL cell_dynamics=bfgs / K_POINTS {automatic} 2 2 2 0 0 0 ATOMIC_SPECIES Si 28.085 Si.pbe-n-kjpaw_psl.0.1.UPF.TXT O 15.999 O.pbe-n-kjpaw_psl.0.1.UPF.TXT ATOMIC_POSITIONS {angstrom} Si 0.000000 0.000000 0.000000 Si 0.000000 0.000000 7.120000 Si 0.000000 7.120000 0.000000 Si 0.000000 7.120000 7.120000 Si 7.120000 0.000000 0.000000 Si 7.120000 0.000000 7.120000 Si 7.120000 7.120000 0.000000 Si 7.120000 7.120000 7.120000 Si 0.000000 3.560000 3.560000 Si 7.120000 3.560000 3.560000 Si 3.560000 3.560000 0.000000 Si 3.560000 3.560000 7.120000 Si 3.560000 0.000000 3.560000 Si 3.560000 7.120000 3.560000 Si 5.340000 1.780000 5.340000 Si 1.780000 1.780000 1.780000 Si 1.780000 5.340000 5.340000 Si 5.340000 5.340000 1.780000 O 0.890000 0.890000 0.890000 O 6.230000 2.670000 4.450000 O 2.670000 4.450000 6.230000 O 4.450000 6.230000 2.670000 O 0.890000 4.450000 4.450000 O 6.230000 6.230000 0.890000 O 2.670000 0.890000 2.670000 O 4.450000 2.670000 6.230000 O 4.450000 0.890000 4.450000 O 2.670000 2.670000 0.890000 O 6.230000 4.450000 2.670000 O 0.890000 6.230000 6.230000 O 4.450000 4.450000 0.890000 O 2.670000 6.230000 4.450000 O 6.230000 0.890000 6.230000 O 0.890000 2.670000 2.670000 O -0.890000 -0.890000 0.890000 O -0.890000 0.890000 -0.890000 O 0.890000 -0.890000 -0.890000 O -0.890000 -0.890000 8.010000 O -0.890000 0.890000 6.230000 O 0.890000 -0.890000 6.230000 O 0.890000 0.890000 8.010000 O -0.890000 6.230000 0.890000 O -0.890000 8.010000 -0.890000 O 0.890000 6.230000 -0.890000 O 0.890000 8.010000 0.890000 O -0.890000 6.230000 8.010000 O -0.890000 8.010000 6.230000 O 0.890000 8.010000 8.010000 O 6.230000 -0.890000 0.890000 O 6.230000 0.890000 -0.890000 O 8.010000 -0.890000 -0.890000 O 8.010000 0.890000 0.890000 O 6.230000 -0.890000 8.010000 O 8.010000 -0.890000 6.230000 O 8.010000 0.890000 8.010000 O 6.230000 8.010000 -0.890000 O 8.010000 6.230000 -0.890000 O 8.010000 8.010000 0.890000 O 6.230000 6.230000 8.010000 O 6.230000 8.010000 6.230000 O 8.010000 6.230000 6.230000 O 8.010000 8.010000 8.010000 O -0.890000 2.670000 4.450000 O -0.890000 4.450000 2.670000 O 8.010000 2.670000 2.670000 O 8.010000 4.450000 4.450000 O 2.670000 4.450000 -0.890000 O 4.450000 2.670000 -0.890000 O 2.670000 2.670000 8.010000 O 4.450000 4.450000 8.010000 O 2.670000 -0.890000 4.450000 O 4.450000 -0.890000 2.670000 O 2.670000 8.010000 2.670000 O 4.450000 8.010000 4.450000 1.) As far as I can tell, SiO2 is a cubic fcc lattice. The Espresso website (http://www.quantum-espresso.org/faq/input-data/#3.1) states that Espresso uses the primitive, rather than conventional, unit cell, unless one specifies otherwise. As I have elected ibrav=2, I infer I am now in the latter category. The directions also state that an all-atom, rather than symmetry-unique atom, representation is chosen. Would I thus specify the Cartesians of 18 Silicon atoms, for an fcc lattice? The code is such that it can recognize the symmetry of the atoms put in, parse out which ones are the unique atoms, and use that symmetry to not re-calculate the same integrals over-and-over, etc.? If it's helpful to visualize, I pulled this structure from a cif file from http://www.crystallography.net/cod/1010954.html 2.) I have specified the lattice constant as celldm(1)=13.454. I assume that the default, Bohr radius, is not affected by selecting the "Angstrom" flag later on. 3.) nat, according the manual, specifies the number of atoms in the unit cell. Does this mean the total number of atoms, i.e., 18+56 for SiO2 if I have selected ibrav=2, or does the code expect the primitive cell atom number since that's the Espresso default? Thank you for your time, Dr. Robert Molt Indiana-University Perdue University ENSCO _______________________________________________ Pw_forum mailing list Pw_forum@pwscf.org http://pwscf.org/mailman/listinfo/pw_forum