* This commit includes the addition of new reference structures such as

ch4: methane-like structure only for binary system.
dia3: diamond structure with primary 1NN and secondary 3NN inteation
tri: H2O-like structure that has an angle
zig: zigzag structure with a uniform angle
lin: linear structure (180 degree angle)

** tri, zig, and lin reference structures require angle information (in degree)
such as the following.
   theta = 109.5