Dear fellow matter modelers, I am trying to model the zig-zag antiferromagnetic material $\alpha$-RuCl$_3$ using QUANTUM ESPRESSO. My end goal is to include DFT + U + SOC, however, including too many of these things together seems to hurt convergence. I am using a supercell with 8 Ru atoms and 32 Cl atoms to accommodate the zig-zag magnetic structure as reported in Phys. Rev. B 92, 235119. I have succeeded in getting the zig-zag magnetic structure to converge without SOC or DFT by first converging for colinear magnetism, then using that as the charge density input for the noncolinear calculation as described in this tutorial. However, when adding a Hubbard_U term to the Ru atoms, the SCF error does not decrease beyond roughly 0.05 Ry. I have tried modifying mixing_beta
, different types of smearing, different k_point grids, and fixing the total magnetization. Any help or advice with this would be appreciated.
Cheers!
My input file is below:
&CONTROL
calculation = 'scf'
outdir = '.'
prefix = 'rucl3'
pseudo_dir = '.'
restart_mode = 'from_scratch'
/
&SYSTEM
A = 5.97620
Hubbard_U(2) = 4.8
Hubbard_U(3) = 4.8
degauss = 0.005
ecutrho = 200
ecutwfc = 50
ibrav = 0
lda_plus_u = .TRUE.
nat = 32
nspin = 2
ntyp = 3
occupations = 'smearing'
smearing = 'gauss'
starting_magnetization(2) = 1
starting_magnetization(3) = -1
/
&ELECTRONS
conv_thr = 1e-6
mixing_beta = 0.1
/
ATOMIC_SPECIES
Cl 35.453 Cl.pbe.ONCVPSP.fr.upf
Ru1 101.07 Ru.pbe.ONCVPSP.fr.upf
Ru2 101.07 Ru.pbe.ONCVPSP.fr.upf
CELL_PARAMETERS alat
1.0000000000000000 0.0000000000000000 0.0000000000000000
0.0000000000000000 1.7305311067233360 0.0000000000000000
-0.6508271189589490 0.0000000000000000 1.9041632824171890
ATOMIC_POSITIONS crystal
Ru1 0.000000000000 0.334410000000 0.000000000000
Ru2 0.000000000000 0.665590000000 0.000000000000
Ru2 0.500000000000 0.834410000000 0.000000000000
Ru1 0.500000000000 0.165590000000 0.000000000000
Ru1 0.000000000000 0.334410000000 0.500000000000
Ru2 0.000000000000 0.665590000000 0.500000000000
Ru2 0.500000000000 0.834410000000 0.500000000000
Ru1 0.500000000000 0.165590000000 0.500000000000
Cl 0.751380000000 0.173500000000 0.383095000000
Cl 0.248620000000 0.173500000000 0.116905000000
Cl 0.248620000000 0.826500000000 0.116905000000
Cl 0.748620000000 0.673500000000 0.116905000000
Cl 0.748620000000 0.326500000000 0.116905000000
Cl 0.751380000000 0.826500000000 0.383095000000
Cl 0.251380000000 0.673500000000 0.383095000000
Cl 0.251380000000 0.326500000000 0.383095000000
Cl 0.751380000000 0.173500000000 0.883095000000
Cl 0.248620000000 0.173500000000 0.616905000000
Cl 0.248620000000 0.826500000000 0.616905000000
Cl 0.748620000000 0.673500000000 0.616905000000
Cl 0.748620000000 0.326500000000 0.616905000000
Cl 0.751380000000 0.826500000000 0.883095000000
Cl 0.251380000000 0.673500000000 0.883095000000
Cl 0.251380000000 0.326500000000 0.883095000000
Cl 0.730230000000 0.000000000000 0.119475000000
Cl 0.269770000000 0.000000000000 0.380525000000
Cl 0.769770000000 0.500000000000 0.380525000000
Cl 0.230230000000 0.500000000000 0.119475000000
Cl 0.730230000000 0.000000000000 0.619475000000
Cl 0.269770000000 0.000000000000 0.880525000000
Cl 0.769770000000 0.500000000000 0.880525000000
Cl 0.230230000000 0.500000000000 0.619475000000
K_POINTS automatic
5 5 5 1 1 1