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====== This page is summary of tricky things (bugs) I found in molecular modeling software ======

===== ESP charges in Dmol3 =====
The new version of Dmol3 provided with Materials Studio (v3.2) has a "new" bug that did not exist in the Cerius2 v4.9:
The ESP charges calculated with a pseudopotential gives awesome results, like charges of +5 or -5 per atom ! The calculations are fine when NOT using any pseudopotential. This bug seems to have been fixed in version 4.0

===== ESP charges in VAMP =====
Vamp is a semi-empirical quantum mecanics program provided with Materials Studio (v3.2). The ESP charges seems to depend on the origin of the coordiates, ie the first atom. This strange feature is probably related with the polar representation of the atoms. This bug does not exist in MOPAC7 (sourceforge version 1.1). In facts I was not even able to reproduce the charges published by the authors Beck, Clark & Glen; [[http://www3.interscience.wiley.com/cgi-bin/abstract/48511/ABSTRACT?CRETRY=1&SRETRY=0|Journal of Computational Chemistry]]
Volume 18, Issue 6 , Pages 744 - 756.

===== Mopac7 =====
  * It is possible to install the MOPAC7 version from sourceforge (v1.10) on Cerius2 v4.9. Just compile it on the SGI computer (with GCC). The results are the same as with MOPAC6 (provided by Cerius2), but twice faster (for ESP charges).
  * When compiled on a AMD64 computer with GCC3.2 ou GCC3.4, the symmetry of the molecule is not determined. The bug may be related to F2C according to Tommi Hassinen (Ghemical)

===== Ghemical =====
This (free) software is  painfull to install (because it needs the latest libraries, especially for OpenGL), nevertheless it seems really promising !

===== X-Ray Powder Diffraction Pattern =====
I compared a hi-resolution XRPD taken at ESRF ID31 with the powder pattern simulated (from single crystal structure)  by some programs. The best result was produces by [[http://www.cryst.chem.uu.nl/platon/pl000000.html|Platon (Spek et al)]] far better than Cerius2 and Materials-studio   from Accelrys. The worse results were obtained by [[http://www.ccdc.cam.ac.uk/products/csd_system/mercury/|Mercury 1.4 and 1.4.1]]. Mercury doe probably not use disordered populations.