[CPMD-list] lattice constant optimization for silicon

[Axel Kohlmeyer]

On Tue, 27 Mar 2007, Yonghyun Kim wrote:

YK> Dear cpmd users.
YK> 
YK>  
YK> 
YK> The single point calculation is done to get the optimized lattice constant
YK> in silicon. 

can you please comment, on _how_ you got the lattice 
constant from a single point calculation?

YK> Here is brief input condition.
YK> 
YK> 2atom supercell/ Cutoff = 60 Ry/ Kpoint sampling= 9x9x9/ Si_MT_LDA.psp/ PCG
YK> optimizer

what settings did you use for the pseudopotential (K-B separation?
which channel as local potential?).

YK> I got a 5.46 angstrom as a lattice constant. 
YK> 
YK> But it seems to be higher than I expect. It should be below 5.43 or
YK> something.
YK> 
YK> Do you have any idea for this?

in most cases unexpected results can be explained by an oversight
in the input or bad parameters (potentials?).

YK> Here is one more thing.
YK> 
YK> How can I define a theoretical melting temperature for certain solids such
YK> as silicon and germanium?

can't help you there. for atomistic simulations (with limited number of 
particles) phase transitions are a big problem, so i always tried to
stay away from them...

cheers,
   axel.

YK> 
YK>  
YK> 
YK> Thank you very much.
YK> 
YK>  
YK> 
YK> Best regards,
YK> 
YK> Yonghyun Kim.
YK> 
YK>  
YK> 
YK> -------------------------------------------------------- 
YK> 
YK> Yonghyun Kim (Ph.D. Student) 
YK> 
YK> Graduate Research Assistant, 
YK> 
YK> - Microelectronics Research Center. 
YK> 
YK>  
YK> 
YK> Dept of Electrical and Computer Engineering. 
YK> 
YK> The University of Texas at Austin. 
YK> 
YK> E-mail: erogen at mail.utexas.edu 
YK> 
YK> Phone: 512) 762 - 5128 
YK> 
YK> -------------------------------------------------------- 
YK> 
YK>  
YK> 
YK>  
YK> 
YK>  
YK> 
YK> 

-- 
=======================================================================
Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
   Center for Molecular Modeling   --   University of Pennsylvania
Department of Chemistry, 231 S.34th Street, Philadelphia, PA 19104-6323
tel: 1-215-898-1582,  fax: 1-215-573-6233,  office-tel: 1-215-898-5425
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If you make something idiot-proof, the universe creates a better idiot.