Visual Molecular Dynamics (VMD) is a very good program for viewing all sorts of structure files.

 

It is free and can be obtained from http://www.ks.uiuc.edu/Research/vmd/ and installed quite easily.

 

You will need to register but that won’t result in enormous amounts of spam.

 

Once installed, it is useful to set the VMDDIR environment variable:

 

>export VMDDIR=/usr/local/vmd                  # or wherever it happens to be

 

and include the directory that contains the executable in your path:

 

>export PATH=$PATH:$VMDDIR/bin

 

The documentation can be found at the above web site or at $VMDDIR/doc/ug.pdf.

 

This program can be a bit slow if run across the network or on a machine that is busily calculating something.

If you are calculating on a remote machine, it can be more convenient to download the appropriate files using scp or sftp to your local machine and run vmd locally.