Dear chimera lovers, Good day. I wrote a small script (pasted below) to monitor the dipole vector of water molecules during MD. The script was adopted based available example. rc('close #1-500') m = chimera.openModels.list()[0] wat = m.residues[2449] com = Point([a.coord() for a in wat.atoms], [a.element.mass for a in wat.atoms]) # dipl = Vector() No working, Use numpy instead dipl = np.array( [0.0,0.0,0.0] ) for atm in wat.atoms: #dipl += atm.charge * atm.coord() dipl += atm.charge * np.array( atm.coord().data() ) vend = np.array(com) + 5 * dipl of = open('current.bild','w') of.write('.color green\n') of.write('.cone %f %f %f %f %f %f 0.5 \n' % (com.x,com.y,com.z,vend[0],vend[1],vend[2])) of.close() rc('open current.bild') Query 1) The following syntax given in a example doesnt work. What is the chimera point object indeed, an array or list ?. How to do math operations on point object. dipl += atm.charge * a.coord() Error: TypeError: unsupported operand type(s) for *: 'float' and '_chimera.Point' Query 2) In my example, I choose a specific water molecule by residue index. I am looking for some way to select the water (or get list of water residues) that satisfy a selection on the fly, lets say that water within 3 A from a prot. residue. In short, how to handle selections inside python script in chimera framework. I tried to play with chimera.selections but I didnt succeed. Any example could be of help. Query 3) Invoke data calculated out of chimera inside a perframe script. If I have say 100 frames. I can do the dipole vector calculation outside chimera and write separate “.bild” files, 1.bild, 2.bild, …..n.bild. Then inside the perframe script, I can invoke a particular .bild fine corresponding to the frame no. Please help me with an syntax example if this is possible. Thanks in advance, Bala -- C. Balasubramanian