[QE-users] how to obtain random initial velocities with CP

[Paolo Giannozzi]

Hi Eduardo

apparently ions_velocities="random" does not set random initial velocities,
but  velocity rescaling. Not sure why. In any event: I am not sure that
starting the CP dynamics from ground-state positions and electrons and
nonzero initial velocities is a good idea.

Paolo

On Sun, Oct 14, 2018 at 8:21 PM Eduardo Menendez <eariel99 at gmail.com> wrote:

> Hi,
> I am unable to start a MD with CP with random velocities setting an
> initial temperature, using QE 6.3. Reading the input description I
> understood that I could start it using              ion_velocities =
> 'random', tempw= starting T. However, I always start with 0 temperature.
>
> This is my output
> &CONTROL
>                  calculation = 'cp' ,
>                 restart_mode = 'restart' ,
>                   pseudo_dir = './' ,
>                         outdir='./tmp',
>                         wfcdir='./tmp',
>                         prefix='mapi',
>                         nstep = 500,
>                            dt = 4.13413733424,
>             ndr = 51,
>             ndw = 51,
>             iprint =50,
>             isave = 50,
> /
> &SYSTEM
>                          ibrav=0,
>                        celldm(1)=1.889726132885 ,
>                           nat=768,
>                         ntyp=5,
>                         ecutwfc=35.0  ! 50,
>                      ecutrho=200.0 ,  ! 180,
>                     input_dft = 'pbesol',
>               nr1b=21, nr2b=21, nr3b=21,  ! nr1b=(2*r_cut)/(Lx)*nr1
>                           nbnd = 1700,
> /
> &ELECTRONS
>                         conv_thr = 1.0e-5,
> !  options for CP
>             emass = 400.d0, ! default, Mosconi et al,PCCP 16,16137 (2014),
> doi: 10.1039/C4CP00569D
>             emass_cutoff = 2.5d0, ! default
>             electron_dynamics = 'verlet' ,
>
> /
>  &IONS
>                 ion_dynamics = 'verlet' , !  'verlet' ,
> !             ion_temperature = 'not_controlled',
>              ion_velocities = 'random',
>                        tempw = 600.0 ,
>  /
> &CELL
>                 cell_dynamics = 'none'
> /
> In the output I read
>    Ionic position will be re-read from restart file
>    All atoms are allowed to move
>    Ionic temperature control via canonical velocities rescaling :
>    temperature required =  600.00000K, tolerance =  100.00000K
> ......
>   nfi     ekinc              temph  tempp     etot
> enthal               econs                econt              vnhh
> xnhh0   vnhp    xnhp0
>       5    0.000002129555068    0.0    0.00  -12738.991035174058
> -12738.991035174058  -12738.991033373713  -12738.991031244159   0.0000
> 0.0000   0.0000   0.0000
>       6    0.000005713182507    0.0    0.00  -12738.991057915813
> -12738.991057915813  -12738.991042309621  -12738.991036596439   0.0000
> 0.0000   0.0000   0.0000
>
> nfi begins at 5 because there were 4 previous steepest descent dynamics
> (ould I reset the nfi counter? ), which got the wfc from a PWSCF
> self-consistent run.
>
> Thanks,
>
> Eduardo Menendez Proupin
> University of Chile
> www.gnm.cl/emenendez
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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