[Pw_forum] decomoposition of the atomic contribution to the vibrational spectrum

[Axel Kohlmeyer]

On Tue, 17 Jul 2007, li niu wrote:

LN> Dear all,

dear niu li (and others that feel, they don't get the help they need),

LN>   I onced asked this problem but could still not solved it. My question
LN>   is about the projection of  vibrational spectrum. 

if you do not get an answer to a question, simply repeating it
will not improve your chances to get an answer. on the contrary,
it may even irritate people.

instead you should ask yourself, why did nobody answer?

perhaps your question was confusing, so you should try to ask
in a different way.

perhaps nobody knows the answer. then repeating the question
will not help.

perhaps nobody is interested in solving your problem. 
then you should try to make it more attractive to solve
your problem.

perhaps your question is so simple, that people think you
can figure it out by yourself. then you should think about
the problem again.

most likely, it is a combination of several of the points
listed above.

LN>  In order to further decompose the carbon contribution to the
LN> vibrational spectrum, as in the paper "Vibrational properties of
LN> trtrahedral amorphous carbon from first principles"[APL
LN> 75,644(1999)], we should define for each bond a "stretching" vector
LN> in the space of the 3N (N is the number of atoms) displacement. The

the most obvious question: did you ask the authors of this paper?
perhaps they already have a solution to your problem?

LN> components of each vector involves the displacement of two atoms in
LN> the direction of the bond and with opposite orientations. We use
LN> these vectors as a
LN>   (non-orthonormal) basis of the stretching subspace and define the bending
LN>   subspace as the complement of the stretching subspace.

what you describe sounds like rather straightforward 
vector/matrix algebra. have you thought about programming
it yourself? 

LN>   My problems:
LN>   How can I construct the stretching subspace and orthorgonalize these
LN>   vectors in 3N space?

well, you essentially wrote what you have to do yourself.

LN>  Which one code may I use?
LN>    
LN>   need your help, any help will be appreciated!

(almost) everybody appreciates help. however, if you
cannot come up with some incentive that motivates people
to help you (an interesting challenge, a project worth
doing, people feeling obliged to help you, because you
were helping them, money, ...), you'll be stuck with 
your problem. this is the kind of contract that you 
enter when using open source software. 

best regards,
    axel.



LN>   best regards!
LN>   
LN>   Niu Li                        
LN>   Harbin Institue of Technology                     
LN>   People's Republic of China
LN>  
LN>  		
LN> ---------------------------------
LN>  Mp3·è¿ñËÑ-иèÈȸè¸ßËÙÏ   

-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
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If you make something idiot-proof, the universe creates a better idiot.