[Pw_forum] Hubbard U and small degauss ...

[Naol Regassa]

Dear all

I have two questions to ask

a) For the last times I was calculating the effect of Hubbard U on the
system YMnO_3 using QESPRESSO 4.10. I got an insulator band structure
using U = 10.5eV though it is completely metal without U (GGA). When I
got this result I have used small degauss = 0.006. My friend told me
to use degauss  = 0.015. Please tell me how possible (correct) is
that? I checked the convergence for degauss but it is increasing near
0.015.

b) Is adding U value more effective for the most stable structure ?
For the unstable states like for my case cubic ferromagnetic phase I
can't see any change?

Here is the input for the 'scf'
&control
    calculation = 'scf',
    restart_mode = 'from_scratch',
    prefix = 'ymo_hcp_ferro'
    tstress = .true.,
    tprnfor = .true.,
    pseudo_dir = '/home/MSC608/Desktop/QESPRESSO_PP',
    outdir='/home/MSC608/Thesis/Hexagonal/Ferro-Hex/temp'
 /
 &system
    ibrav = 0,
    celldm(1) = 6.7,
    nat =  10,
    ntyp = 4,
    ecutwfc = 32,
    ecutrho = 340.0
    nspin = 2
    starting_magnetization(2) = 0.7,
    starting_magnetization(3) = 0.7,
    occupations = 'smearing',
    smearing = 'marzari-vanderbilt',
    degauss = 0.005,
    lda_plus_u=.true.,
    Hubbard_U(2) = 10.5,
    Hubbard_U(3) = 10.5,
 /
 &electrons
    diagonalization = 'david'
    startingwfc = 'atomic+random'
    mixing_beta = 0.3,
    conv_thr =  1.0d-10
 /
 ATOMIC_SPECIES
  Y     88.91     Y.pbe-nsp-van.UPF
  Mn1   54.94     Mn.pbe-sp-van_mit.UPF
  Mn2   54.94     Mn.pbe-sp-van_mit.UPF
  O     15.9994   O.pbe-rrkjus.UPF

CELL_PARAMETERS (alat)
   0.985236441  -0.266531554  -0.000316189
  -0.266366323   0.985859979   0.000349871
   0.000781869  -0.000890980   3.186836665

ATOMIC_POSITIONS (crystal)
Y       -0.082663260  -0.082649328   0.000174846
Y       -0.082874577  -0.082880779   0.499813069
Mn1      0.205305857   0.560245090   0.249986248
Mn2      0.561457263   0.207812583   0.750012603
O       -0.027464907  -0.056329933   0.249979343
O       -0.058482388  -0.031289340   0.750035308
O        0.247951998   0.582250730   0.083800805
O        0.582338704   0.248188482   0.916046842
O        0.582135578   0.247948396   0.583964864
O        0.247742343   0.582041831   0.416186070
  K_POINTS automatic
  3 3 2  1 1 1

Thanks alot in  advance
 Tamene Regassa
 AAU
 Ethiopia