ref:
Graph theory meets Ab Inito MD: atomic structures and transformations at the nanoscale.
		PRL 107,085504(2011)

xyz:	3*n
graph:	n  

Accurate for big cluster but bad for small molecular.

dsyev:
A * v(i)^T = lamda(i) * v(i)^T
after dsyev A=[v(1)^T,v(2)^T,...]