[Pw_forum] Application of LDA+U in phonon calculations.

[W2AGZ]

Hi Saswata,

WRT your question 2, I have posted on the forum for several years pointing out the lack of a tool to calculate e-p interaction in the context of LDA+U.  Such a tool is badly needed within QE and supporting response function packages such as Yambo.   I've been told the tool may be available in the ELK package, but have not had the opportunity to check this out yet. 

-Paul Grant
W2AGZ Technologies.

-----Original Message-----
From: pw_forum-bounces at pwscf.org [mailto:pw_forum-bounces at pwscf.org] On Behalf Of saswata halder
Sent: Thursday, September 24, 2015 11:59 AM
To: PWSCF Forum
Subject: [Pw_forum] Application of LDA+U in phonon calculations.

Dear All,

At present I am trying to calculate the phonon modes of double perovskite Ba2SmTaO6 having a cubic Fm3m structure. The detailed input of the vc-relax file is provided below (and also attached alongwith).

 &CONTROL
    calculation='vc-relax',
    restart_mode='from_scratch',
    prefix='BST'
    pseudo_dir = '/home/saswata/espresso/potentials/',
    outdir='./'
    tstress=.true.
    tprnfor=.true.
    verbosity='high'
    wf_collect=.true.
    nstep=200
    etot_conv_thr=1.0D-7
    forc_conv_thr=1.0D-4
    disk_io='default'
 /
 &SYSTEM
    ibrav = 2, celldm(1) =16.0208, nat = 10, ntyp= 4,
    ecutwfc = 80.0, ecutrho=800, occupations='smearing',
    smearing='gaussian', degauss=0.02, nspin=2,
    starting_magnetization(2)=0.4,
    lda_plus_u=.true.,
    Hubbard_U(2)=7.0,

 /
 &ELECTRONS
    diagonalization='david',
    mixing_mode='plain',
    mixing_beta = 0.7D0
    conv_thr =  1.0D-9
    electron_maxstep=200
 /
&IONS
    ion_dynamics='bfgs'
    upscale=10D0
    trust_radius_max=1.0D0
    trust_radius_min=1.0D-5
    trust_radius_ini=0.5D0
    w_1=0.01D0
    w_2=0.5D0
/
&CELL
    cell_dynamics='bfgs',
    press=0.0,
    cell_factor=2.5D0,
    press_conv_thr=0.2,
/
ATOMIC_SPECIES
 Ba  137.327    Ba.pbe-mt_fhi.UPF
 Sm  150.360    Sm.pbe-mt_fhi.UPF
 Ta  180.94788  Ta.pbe-mt_fhi.UPF
 O   15.9994     O.pbe-mt_fhi.UPF
ATOMIC_POSITIONS crystal
 Ba 0.25  0.25  0.25
 Ba 0.75  0.75  0.75
 Sm 0.00  0.00  0.00
 Ta 0.50  0.50  0.50
 O  0.264 0.00  0.00
 O  0.736 0.00  0.00
 O  0.00  0.264 0.00
 O  0.00  0.736 0.00
 O  0.00  0.00  0.264
 O  0.00  0.00  0.736
K_POINTS automatic
    4 4 4  1 1 1

  I specifically have two questions regarding the output of this calculation

1. The structural relaxation occurs but with a pressure value of P=-13.71. What is the significance of this negative pressure?

2. The phonon calculation terminates with an error message 'LDA+U is not implemented in phonon'. Is there any other way to go about with this calculation in the existing QE versions?

Thanking you in advance and awaiting a reply eagerly,

Saswata Halder.

Senior Research Fellow

Bose Institute.