[Chimera-users] [External] Re: in *.gro file, chimera takes CL atom as C (in compound) and gives it wrong color

Eric Pettersen pett at cgl.ucsf.edu
Mon Mar 22 10:52:44 PDT 2021

Hi Lei,
	If all your chlorine atom names start with the characters "CL", you can change them all to chlorine after you open the .gro file with this command (Favorites→Command Line):

	setattr a element Cl @CL=


	Eric Pettersen
	UCSF Computer Graphics Lab

> On Mar 21, 2021, at 7:54 PM, Lei Qian <tuk04130 at temple.edu> wrote:
> Hi Eric, 
> Sorry for my late reply.
> Yes you are right.
> I tried it again: I made a new gro file containing only CL and K as ions, and opened it using chimera. 
> I found chimera colored K as violet, which is good; but it colored CL as the same color as Carbon: yellow.
> Thank you again for your help!
> Best,
> Lei
> On Tue, Feb 23, 2021 at 5:04 AM Eric Pettersen <pett at cgl.ucsf.edu <mailto:pett at cgl.ucsf.edu>> wrote:
> Hi Lei,
> 	There is no explicit indication of the chemical element type in a .gro file, so it's all guesswork.  Chimera assumes that atom names that begin with any of the letters C, O, P, S, H, or N are the corresponding single letter element type.  This prevents atom names like CA and HG from being interpreted as calcium and mercury, rather than carbon and hydrogen.
> 	There aren't any great solutions.  One option is to read in the .gro file, write it out as a .mol2 file, then edit that file to change the atom type of the CL atoms to Cl, then read that back in.  Another is to select your CL atoms and use the "Modify Structure" tab of the Build Structure tool to change their element to Cl.
> --Eric
> 	Eric Pettersen
> 	UCSF Computer Graphics Lab
>> On Feb 18, 2021, at 8:30 PM, Lei Qian <tuk04130 at temple.edu <mailto:tuk04130 at temple.edu>> wrote:
>> Dear users,
>> Could I ask a question on chimera? Thanks!
>> I tried to open a gro file (small compound) using chimera. Like below:
>> ... ...
>>     1  LIG   CL   18   x.xxx    x.xxx      x.xxx  
>>     1  LIG  CL1   19   x.xxx    x.xxx      x.xxx    
>> ... ...
>> Although chimera shows the CL name "CL" when the cursor is above the atom, but the CL atom color is incorrect: the same as Carbon. 
>> I tried to change the "CL" to "BR", and the chimera shows the correct color: dark red. It seems weird to me. Could you please give me any suggestions? 
>> Thanks!
>> Best,
>> Lei
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