CCL: classification of MOs as sigma and pi orbitals reg

["Rajagopala Reddy Seelam" <rajagopalaseelam() gmail.com>]

 Sent to CCL by: "Rajagopala Reddy Seelam" [rajagopalaseelam _
 gmail.com]
 Respected CCL Administrators and subscribers,
 How can we classify a molecular orbital as sigma(sigma*), pi(pi*) and n(n*). If
 the basis set used in the abinitio calculation is small (like sto-3g and 3-21g)
 it is easy. But if we use large basis is task is not as straight forward as the
 previous one. Are there any rule of thumb available to classify a molecular
 orbital as sigma, pi etc.
 Can we use NBO analysis to get these.
 Please excuse me if my question is naive.