FEATURE CHANGE: atoms without vibration will no longer report out as vxyz = {0 0 0} or vx = 0
-- print {atomno=3}.vxyz and {*}.vxyz.all will report -1
instead of {vx vy vz} when atom does not have a vibration
-- print {atomno=3}.vx will report "NaN" (also vy and vz)
-- label %[vxyz] will be blank
-- label %[vx] will be blank (also vy and vz)
-- select vxyz >= 0 will select for atoms with vibrations of any magnitude
-- select vxyz < 0 will select for atoms without vibrations of any magnitude
-- select vx = 0 will NOT select atoms with no vibration vector
-- select vx != 0 will NOT select atoms with no vibration vector
-- select vx = 0 || vx != 0 will select for atoms with vibrations of any magnitude
-- same with modulations and modxyz, modx, mody, modz