Subject: FTs of various ACFs

From: Dr Malcolm E Parker <[email-masked]>
Date: Tue, 18 Feb 1997 14:26:24 +0000 (GMT)

Hi.
   Hope someone here can help as I've had my colleagues scratching their 
heads all day.I have calculated the Fourier transforms of various ACFs 
obtained from MD simulations of water (bondlengths, angles, velocities 
etc). This has been done both by 'brute force' and via a FFT routine. The 
problem I am having is that there is a small constant baseline shift. Is 
this an error or a genuine effect? Also, some of the peaks are positive 
going, some negative going and some both. I am having poblems coming to 
terms with the concept of 'negative densities of states'. What do these 
signs physically represent, or is it just mathematical artifice ? The 
FORTRAN abs() function is not really an option here ;-)

Thanks in advance for your help.

-MAL

 -- 

Dr Malcolm Parker               | email: [email-masked]
Department of Chemistry,        | www:   http://www.chem.surrey.ac.uk/~chs1mp
University of Surrey,           |
Guildford, Surrey. GU2 5XH. UK. | Tel: (01483) 300800x2580  Fax: (01483) 259514
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