I always forget how to change the image size for rending molecular images in VMD using the (external) Tachyon rendering engine, so I thought I'd write down the steps here:

In the TCL console, get the aspect ratio correct for the image. So, for example to make a nice 1920x1080 image, we'll make the view at half of that:

 
display resize 960 540

Now, add simply add -res 1920 1080 to the end of the render command in the file render controls window. Here's an example of one of my render commands:
 
"$HOME/VMD/tachyon_LINUXAMD64" -aasamples 12 %s -format TARGA -o %s.tga -res 1920 1080

Here's the result of one my renders:

Nice picture. What are the graphical representation specifications (material, coloring method, etc)?

Thank you! CPK is rep. Coloring was by atom. I changed the default atom colors (dark gray hydrogen, gray carbon, red oxygen, blue nitrogen). The material is AOChalky with an outline added.