[Chimera-users] Handling electrostatic potential in cube format

[Elaine Meng]

Hi Boaz, 
Regarding your later message: yes, APBS .dx is a known ESP format for Chimera and ChimeraX, along with UHBD .grd and DelPhi(academic version)/GRASP .phi:

<http://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/filetypes.html#esp>
<http://rbvi.ucsf.edu/chimerax/docs/user/commands/open.html#volume>

There isn’t any “fitting” per se with the known grid formats, the coordinates are read directly from information in the file.  So it sounds like the cube file from DelPhi may be similar enough to the known format that it is read, but some difference prevents correct interpretation of the grid offset or scale.  If you are OK with using APBS dx instead, never mind, but re this Delphi cube file, if you have a non-private one, you could use Help… Report a Bug (in Chimera menu) and attach an example cube file and say in the description which PDB ID it goes with. 

Somewhat of an aside: in Volume Viewer menu: Features… Coordinates, you can specify grid origin and spacing, but that means you would have to know what values to enter in the first place.
<http://www.rbvi.ucsf.edu/chimera/docs/ContributedSoftware/volumeviewer/volumeviewer.html#coordinates>

Best,
Elaine 
-----
Elaine C. Meng, Ph.D.                       
UCSF Chimera(X) team
Department of Pharmaceutical Chemistry
University of California, San Francisco

> On May 4, 2019, at 2:51 PM, Boaz Shaanan <bshaanan at bgu.ac.il> wrote:
> 
> Hi,
> It seems as if the new Delphi version (v8.4) only knows to produce potential phi files in cube format. Oh well. I'm beginning to play with this format via the volume viewer but so far the fit of the surface to the atomic model is bad, let alone that potential values on the surface (as reported by moving the mouse on the surface) make no sense. I'm wondering whether there is a chance to achieve as nice a fit of the cube surface to the protein model as is easily achieved with the good old .phi format and surface command. So far I'm lost. I'd appreciate any clues. 
> 
> Luckily, I still keep the older version but there might be some improvements in the potential calculations in the newer version.
> 
> Thanks for your help.
>      Boaz
>