>Uii should be positive and greater than 0 to make physical sense.
Yes. In particular Uij should be a positive definite matrix. If Uii is
negative it means that some systematic error is being soaked up there
eg lack of an absorbtion correction will reduce the apparent temperature
factor, since absorbtion tends to reduce intensity most at lower angles.
>Moreover, there are other restrictions too...
To obtain the relations between Bij for special atom positions, apply
the symmetry operations one by one to the atom; if the operation
leaves the atom invariant, it must also leave it's Bij invariant when
you apply it to the B-factor matrix.
Alan H.
Alan Hewat, ILL Grenoble, FRANCE <[EMAIL PROTECTED]> tel (33) 4.76.20.72.13
ftp://ftp.ill.fr/pub/dif fax (33) 4.76.48.39.06 http://www.ill.fr/dif/
