[QE-users] Problem in fixing selected atomic positions in "vc-relax" calculation

[Shoaib Muhammad]

Hi,

 �

I am trying a “vc-relax” calculation in which I want to fix some of the atomic positions because these are the special positions in the crystal structure but during vc-relax calculation these atomic positions are not kept fixed instead these positions also vary after each iteration. I am using QE ver 6.3. Is it the normal behavior for “vc-relax” calculation that we cannot fix selected atomic positions or am I doing some mistake in the input file?

 �

My input file looks like this:

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&CONTROL

    calculation        = "vc-relax"

    forc_conv_thr  =  1.00000e-03

    max_seconds   =  1.72800e+05

    nstep                 = 100

    pseudo_dir       = "/home/pseudo"

/

 �

&SYSTEM

    a                                              =  5.01090e+00

    b                                              =  8.66290e+00

    c                                              =  5.09222e+00

    cosac                                      = -3.33412e-01

    degauss                                 =  1.00000e-02

    ecutrho                                  =  2.20000e+02

    ecutwfc                                 =  5.50000e+01

    hubbard_u(2)                       =  3.90000e+00

    ibrav                                       = 0

    lda_plus_u                            = .TRUE.

    nat                                          = 24

    nspin                                      = 2

    ntyp                                        = 3

    occupations                          = "smearing"

    smearing                               = "gaussian"

    starting_magnetization(1) =  0.00000e+00

    starting_magnetization(2) =  2.00000e-01

    starting_magnetization(3) =  0.00000e+00

/

 �

&ELECTRONS

    conv_thr                 =  1.00000e-06

    electron_maxstep = 200

    mixing_beta           =  4.00000e-01

    startingpot             = "atomic"

    startingwfc            = "atomic+random"

/

 �

&IONS

    ion_dynamics = "bfgs"

/

 �

&CELL

    cell_dynamics    = "bfgs"

    press_conv_thr =  5.00000e-01

/

 �

K_POINTS {automatic}

2  1  2  0 0 0

 �

CELL_PARAMETERS {angstrom}

  5.010900   0.000000   0.000000

  0.000000   8.662900   0.000000

-1.697807   0.000000   4.800849

 �

ATOMIC_SPECIES

Li        6.94100  Li.pbe-s-kjpaw_psl.1.0.0.UPF

Mn     54.93805  Mn.pbe-spn-kjpaw_psl.1.0.0.UPF

O        15.99940  O.pbe-n-kjpaw_psl.1.0.0.UPF

 �

ATOMIC_POSITIONS {crystal}

Li      0.000000   0.338869   0.500000  0 1 0

Li      0.000000   0.661131   0.500000  0 1 0

Li      0.500000   0.838869   0.500000  0 1 0

Li      0.500000   0.161131   0.500000  0 1 0

Li      0.000000   0.000000   0.500000  0 0 0

Li      0.500000   0.500000   0.500000  0 0 0

Li      0.000000   0.500000   0.000000  0 0 0

Li      0.500000   0.000000   0.000000  0 0 0

Mn   0.000000   0.167106   0.000000  0 1 0

Mn   0.000000   0.832894   0.000000  0 1 0

Mn   0.500000   0.667106   0.000000  0 1 0

Mn   0.500000   0.332894   0.000000  0 1 0

O       0.245825   0.178664   0.776064

O       0.754168   0.821336   0.223935

O       0.754168   0.178664   0.223935

O       0.245825   0.821336   0.776064

O       0.745825   0.678664   0.776064

O       0.254167   0.321336   0.223935

O       0.254167   0.678664   0.223935

O       0.745825   0.321336   0.776064

O       0.219093   0.000000   0.227663  1 0 1

O       0.780899   0.000000   0.772336  1 0 1

O       0.719094   0.500000   0.227663  1 0 1

O       0.280899   0.500000   0.772336  1 0 1

 �

 �

Thanks,

 �

Shoaib Muhammad

Post-Doctoral Research Fellow

Department of Energy Science

Sungkyunkwan University

Korea

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