How can I know if 3D aperiodic systems are not interacting with each other using Quantum ESPRESSO?

I wanted to observe the Projected Density of States of InP system passivated with Hydride ions. For that, the following input file was created.

&CONTROL
calculation='scf',
outdir='./outdir',
prefix='InPH',
pseudo_dir='.',
verbosity='low',
tprnfor=.true.,
tstress=.true.,
/
&SYSTEM
ibrav = 0
A =   28.95873
nat = 38
ntyp = 3
ecutwfc=50,
ecutrho=400,
input_dft='pbe',
occupations='smearing',
starting_charge(1) = +3.0
starting_charge(2) = -3.0
starting_charge(3) = -1.0
smearing='mv',
degauss=0.005d0,

/

&ELECTRONS
conv_thr=1d-07,
mixing_beta=0.7d0,
/

CELL_PARAMETERS {alat}
1.000000000000000   0.000000000000000   0.000000000000000
0.000000000000000   1.000000000000000   0.000000000000000
0.000000000000000   0.000000000000000   1.000000000000000
ATOMIC_SPECIES
In  114.81800   In.pbe-dn-kjpaw_psl.1.0.0.UPF
P   30.97300   P.pbe-n-kjpaw_psl.1.0.0.UPF
H    1.00750   H.pbe-kjpaw_psl.1.0.0.UPF
ATOMIC_POSITIONS {crystal}
In   0.301777000000000   0.515510000000000   0.403224000000000
In   0.489752000000000   0.303558000000000   0.415264000000000
In   0.503499000000000   0.505059000000000   0.408072000000000
In   0.501909000000000   0.513929000000000   0.598334000000000
In   0.296909000000000   0.419582000000000   0.514790000000000
In   0.492873000000000   0.398390000000000   0.315705000000000
In   0.497050000000000   0.408959000000000   0.504514000000000
In   0.510066000000000   0.608991000000000   0.499706000000000
In   0.390717000000000   0.315763000000000   0.518452000000000
In   0.401476000000000   0.501161000000000   0.310056000000000
In   0.402099000000000   0.515299000000000   0.498794000000000
In   0.602463000000000   0.505451000000000   0.505306000000000
In   0.393310000000000   0.407603000000000   0.415739000000000
In   0.399042000000000   0.422615000000000   0.605304000000000
In   0.406187000000000   0.607978000000000   0.395822000000000
In   0.594811000000000   0.396109000000000   0.407363000000000
P   0.448966000000000   0.459054000000000   0.454312000000000
P   0.440175000000000   0.354263000000000   0.367464000000000
P   0.445543000000000   0.367260000000000   0.559101000000000
P   0.455293000000000   0.551606000000000   0.354347000000000
P   0.454803000000000   0.563518000000000   0.546515000000000
P   0.348592000000000   0.457212000000000   0.361770000000000
P   0.351886000000000   0.472249000000000   0.553642000000000
P   0.546899000000000   0.448683000000000   0.359923000000000
P   0.548477000000000   0.458559000000000   0.552198000000000
P   0.341560000000000   0.363924000000000   0.467769000000000
P   0.354314000000000   0.565300000000000   0.448689000000000
P   0.543486000000000   0.352663000000000   0.460158000000000
P   0.556644000000000   0.554867000000000   0.452761000000000
H   0.642987000000000   0.469927000000000   0.474034000000000
H   0.481225000000000   0.651348000000000   0.464263000000000
H   0.255512000000000   0.450777000000000   0.480210000000000
H   0.526102000000000   0.358078000000000   0.281589000000000
H   0.522877000000000   0.266367000000000   0.377674000000000
H   0.360938000000000   0.390592000000000   0.642932000000000
H   0.271709000000000   0.550732000000000   0.361406000000000
H   0.371546000000000   0.639032000000000   0.354239000000000
H   0.367327000000000   0.536759000000000   0.271849000000000

K_POINTS {automatic}
1 1 1  0 0 0


Here the quantum dot has 13 P$$^{-3}$$ ions, 16 In$$^{+3}$$ ions and 9 H$$^{-}$$. Hence the starting charge.

How can I know if the systems are not interacting with each other? The diameter of the system is 8 angstrom and the unit cell is cubic with a cell parameter of 28 angstroms

NOTE: The convergence of observables w.r.t variation in Cell parameters (as Tristan suggested) is one method. But if there are other more quantifiable methods like calculating the electron density in between two particles in adjacent cells, it would be nice to know :)

Thanks in Advance!!

1 Answer

Since QE is a planewave based code and we are talking about cells, its important to realize its periodic so its always interacting with itself to some degree. The only way to check if its sufficiently not interacting is to increase the cell size and see if your property changes. If it does, repeat again until its converged just like kpoints or energy cutoffs.

• +1, Thank You for your answer! This is correct but rather than identifying the parameters for minimal interaction by the variation in the observables wrt cell size, I was hoping if there was a method to observe the real space electron density around the particle. – Anoop A Nair Jan 17 at 10:44
• Hmm someone may know around here, this seems like something that could have an answer along those lines. – Tristan Maxson Jan 17 at 19:05
• I don't know if QE is able to do the following. SIESTA, that it is also for periodic system (is mandatory to input the crystal parameters), is able to detect the type of system from the atom configuration and cell parameters. It can detect if the system is a molecule, a slab, or a crystal and then, treat accordingly. – Camps Jan 18 at 0:22