[CPMD-list] Temperature simulations

[Veronique Van Speybroeck]

Dear Ari,

thanks for your suggestions.  First of all I gave the atoms a random 
displacement of 0.05 by the option randomize in the inputfile and then 
did again a geometry optimization.  The programs ends normally, but the 
atoms do not return to their original position, the energy however is 
converged.  I must conclude then that the system is indeed unstable. 
 The input file is given below of this simulations.  By the way I did 
not optimize the cell parameters, is this necessary?  

Now some simulations run on the larger system.  this takes longer so I 
do not know the result yet.  

Is it an option to use the nose keyword for the electrons to keep them 
close to the BO surface?  
Then the question remains how to choose this electronic mass?  

Thanks in advance
veronique

PS : the thing movie sample is for some conversion programs that I have 
written.  They transform the MOVIE file into car and arc files which can 
be read in by CERIUS.



input file for geometry optimization :
&CPMD
 RESTART LATEST WAVEFUNCTION
 OPTIMIZE GEOMETRY
 TIMESTEP
  5
 MAXSTEP
  3000
 PRINT
  10
 RANDOMIZE COORDINATES
  0.05
 STRUCTURE BONDS ANGLES
 MOVIE SAMPLE
  1
&END

&SYSTEM
 ANGSTROM
 SYMMETRY
 1
 CELL
 6.3 1.0 1.0 0.0 0.0 0.0
 CUTOFF
 25.
&END

&ATOMS
*Cl_VDB_U BINARY NEWF
 LMAX=P
 4
 0.000000    0.000000    0.000000
 3.150000    0.000000    3.150000
 0.000000    3.150000    3.150000
 3.150000    3.150000    0.000000
*019-K-ca-sp-vgrp.uspp BINARY NEWF
 LMAX=P
 4
 3.150000    3.150000    3.150000
 0.000000    0.000000    3.150000
 0.000000    3.150000    0.000000
 3.150000    0.000000    0.000000
&END

&DFT
 LDA CORRELATION PZ
 FUNCTIONAL BP
 GC-CUTOFF
 5.D-5
&END



Ari.P.Seitsonen at iki.fi wrote:

>Dear Veronique,
>
>  Some suggestions:
>
> - The system is too small for Gamma point only, it might be that the
>   ionic configuration is unstable; you could test this by giving the
>   ions a small displacement from the equilibrium positions (by the
>   way, for such crystals I find the keyword 'SCALED' very useful) and
>   then relax the geometry and see, if the atoms return to the lattice
>   positions. The natural solution, if the structure is indeed
>   unstable, is to use a bigger cell (2x2x2, i.e. 32 atoms of each
>   species)
>
> - You don't specify the electronic mass, the default might be
>   unsuitable for this system (also the electrons heat up slowly in
>   your simulation)
>
>  Please tell if this doesn't help, then we can try something else.
>
>    Greetings,
>
>       apsi
>
>PS I guess that you use the option 'MOVIE SAMPLE \n 1' only for the
>  debugging, right?
>
>  
>
>>I have some problems simulating the KCL lattice at elevated temperature. 
>> First I did an optimizations on the lattice.  Next I tried to heat up 
>>the crystal with the inputfile as given below.  Normally I would expect 
>>only small oscillations of the atoms around their equilibrium positions, 
>>due to the low temperature.  Strangely the atoms undergo very large 
>>variations and I get a totally distorted system.  The temperature in the 
>>ENERGIES file raises also drastically.  Can somebody tell me what I do 
>>wrong?  The energies file is given in attachment.  
>>When I do a MD simulations microcanonically, everything goes fine and 
>>the system stays in the minimuum.
>>
>>Thanks in advance
>>
>>veronique
>>
>>
>>&CPMD
>> RESTART LATEST WAVEFUNCTIONS
>> MOLECULAR DYNAMICS CP
>> TIMESTEP
>>  5
>> MAXSTEP
>>  2000
>> PRINT
>>  10
>> TEMPERATURE
>>  5
>> QUENCH BO
>> STRUCTURE BONDS ANGLES
>> MOVIE SAMPLE
>>  1
>>&END
>>
>>&SYSTEM
>> ANGSTROM
>> SYMMETRY
>> 1
>> CELL
>> 6.3 1.0 1.0 0.0 0.0 0.0
>> CUTOFF
>> 25.
>>&END
>>
>>&ATOMS
>>*Cl_VDB_U BINARY NEWF
>> LMAX=P
>> 4
>> 0.000000    0.000000    0.000000
>> 3.150000    0.000000    3.150000
>> 0.000000    3.150000    3.150000
>> 3.150000    3.150000    0.000000
>>*019-K-ca-sp-vgrp.uspp BINARY NEWF
>> LMAX=P
>> 4
>> 3.150000    3.150000    3.150000
>> 0.000000    0.000000    3.150000
>> 0.000000    3.150000    0.000000
>> 3.150000    0.000000    0.000000
>>&END
>>
>>&DFT
>> LDA CORRELATION PZ
>> FUNCTIONAL BP
>> GC-CUTOFF
>> 5.D-5
>>&END
>>    
>>
>
>  
>

-- 
-----------------------------------------------------------------------
Dr. ir. Van Speybroeck Veronique
Laboratorium voor Theoretische Fysica
Universiteit Gent
Proeftuinstraat 86
9000 Gent
Tel +32-9-264.65.58  GSM : +32/474/259767
Fax +32-9-264.65.60
email : veronique.vanspeybroeck at rug.ac.be
http://inwfaxp2.rug.ac.be/~web/onderzoek/proj_3.html
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