Subject: RE: Problem with HyperNMR

From: Joel Polowin <[email-masked]>
Date: Thu, 28 Aug 1997 09:05:50 -0400

Adnan Hazar <[email-masked]> writes:

> From: Serge Pachkovsky <[email-masked]>
> 
> In your particular case, there are 64 atoms and 145 orbitals, so the
> shilding tensor calculation should need from 2Mb (for a "generous"
> implementation) to 93Mb (for a "wasteful" one). Coupling constants
> might need from 32Mb to 132Mb, possibly in addition to the shielding
> tensor requirements. Keep in mind what these are back-of-the-envelope
> estimations, actual requirements may differ by a factor of 2 or four
> in either direction, depending on the actual implementations' quality.

The problem is not (or should not be) with the calculation of the
shielding tensors and coupling constants -- that should be no real
problem for a system of this size.  (As you noted in your earlier
message, this calculation is completed successfully in a couple of
minutes.)  But the calculation of the spectrum from those values has 
an (approximately) exponential dependence on the number of spin states.

Or so I believe; I have never understood the details of those
calculations very well.

It is possible to do the first calculation on many atoms, save the 
results in a file, and then edit that file to reduce the "NMR Atom"
set so that the spectrum is calculated only for fewer atoms.  This
is not a trivial editing job, however, since you would need to remove
blocks of arrays of numbers.  What HyperNMR really needs is a way of
defining a further subset of "NMR Atoms" -- "Spectrum Atoms".  I had
suggested something like that to the developer, but there wasn't time
to implement it before the last software release.

Joel Polowin
[email-masked]