[CPMD-list] Geometry optimization and misrepresentation of the x-ray data...

[Pedro Nuno Simões]

Dear Ewald

Thank you for you prompt reply. Here it goes the input (hope enough). 
All coordinates came from X-ray data (CIF file). I should say that the 
single point calculation (OPTIMIZE WAVEFUNCTION) has run without problems.

Thanks again,
Pedro.

-----------------------------------
!  Sample LD01
!
 &CPMD
    OPTIMIZE GEOMETRY XYZ
    RESTART WAVEFUNCTION COORDINATES LATEST
    LBFGS
    CONVERGENCE ADAPT
     0.02
    CONVERGENCE ENERGY
     0.05
    HESSIAN DISCO
 &END
 &DFT
 FUNCTIONAL BLYP
 &END
 &SYSTEM
   ANGSTROM
   CELL ABSOLUTE VECTORS
     9.304 0.0 -6.10537904 0.0 6.6665 0.0 0.0 0.0 10.07482858
   CUTOFF
     120
   POINT GROUP
     5
 &END
 &ATOMS
*C_SG_BLYP
 LMAX=D
 12
(...)
*N_SG_BLYP
 LMAX=D
 4
(...)
*O_SG_BLYP
 LMAX=D
 12
(...)
*Cl_SG_BLYP
 LMAX=D
 4
(...)
*H_SG_BLYP
 LMAX=S
 32
(...)
   CONSTRAINTS
     FIX SEQUENCE
       1 32
   END CONSTRAINTS
 &END
-----------------------------------

Ewald Pauwels escreveu:
> Dear Pedro,
>
> It looks like you might have made some mistakes in defining the 
> periodicity of your crystal.
> But please include your inputfile in your post, otherwise people won't 
> be able to help you.
>
> Sincerely,
> Ewald.
>
>
>
> Pedro Nuno Simões wrote:
>> Dear CPMD users.
>>
>> I am a beginner, with a basic experience in CPMD. Now, I am trying to 
>> further expand my capabilities in using the code.
>> For now I am using CPMD toward the vibrational analysis of organic 
>> crystalline systems, based on X-ray data. The main problem I am 
>> facing occurs in geometry optimizations. I was expecting that 
>> optimization essentially resulted in the correction of protonic 
>> positions. This was not the case, preventing any reliable comparison 
>> with experimental vibrational data.
>>
>> I have tried several approaches summarized below for a representative 
>> system.
>> (1) A cell including 4 complete cations and 4 chlorine anions was 
>> created based on x-ray information.
>> Looking to the "trajectory" corresponding to the optimization steps, 
>> a dramatic structural change was observed, involving 
>> cleavage/formation of protonic bonds.
>> (2) I repeated the procedure describe in (1) but by fixing the heavy 
>> atoms according to a CONSTRAINTS|FIX SEQUENCE specification. The same 
>> problem was encountered.
>> (3) I decided to repeat the above scheme by defining the initial 
>> geometrical parameters directly from CIF data (i.e., without any 
>> reconstruction of complete fragments within the cell, as attempted in 
>> (1) and (2). The result was identical to those from the previous cases.
>> (4) Finally I tried the same as in (3) but using POINT GROUP=5 
>> (according to X-ray data) instead of POINT GROUP=AUTO in the SYSTEM 
>> section. In this case, I allowed the optimization to be finished and 
>> after vibrational analysis has been performed. The results are quite 
>> doubtful.
>>
>> I look forward to any kind of  help.
>> Thanks in advance,
>> Pedro.
>>
>>   
>
>


-- 
----------------------
Pedro Nuno N.L. Simões

Departamento de Engenharia Química
FCTUC-Pólo II
Rua Sílvio Lima
3030-790 Coimbra
Portugal

Telef.: +351 239 798 732
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