X-PLOR electron density data files

Christian Lemmen lemmen at gmd.de
Tue Jul 21 15:40:52 EST 1998

Hi everybody!

I`ve some simple questions concerning the X-PLOR electron-density-output
I hope this is the propper community to ask these questions. If not,
would anybody please be so
kind and tell me whome I might ask instead?

I've got to extract data from X-PLOR electron-density-output files
for other purposes. The header of such files contains a lot of
stuff. Is the following correct?

a = legth of unit cell in direction a (in Angstr"om)
b = legth of unit cell in direction b (in Angstr"om)
c = legth of unit cell in direction c (in Angstr"om)
alpha = angle between b and c
beta = angle between a and c
gamma = angle between  a and b

AN = number of intersections of a
AMIN, AMAX data is given between min and max in direction a
BN = number of intersections of b
BMIN, BMAX data is given between min and max in direction b
CN = number of intersections of c
CMIN, CMAX data is given between min and max in direction c


a=10, b=10, c=10, alpha-90, beta=90, gamma=90
(cube with side length 10 Angst"om)

AN = BN = CN = 10
(the grid spacing is 1 Angtr"om the following grid points are defined:
     4,4,4   4,4,5   4,4,6   ...   4,4,12
     4,5,4   4,5,5   4,5,6   ...   4,5,12
     12,12,4 12,12,5 12,12,6 ... 12,12,12)

The second question concerns the data given at the grid points:
     Does each value on the grid represent an electron density level
     at the respective point in space? If yes, why are then plenty of
     the values negative? If no, what do these values represent?

I'd be glad to receive any useful information on this subject.


Christian Lemmen (Lemmen at gmd.de)

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