How does ICM calculate hydrogen bond acceptor property?

[Andrew Orry]

Q. How does ICM calculate hydrogen bond acceptor property?

A. Atom is considered as Hydrogen Bond Acceptor if :

* any oxygen
* sp1 nitrogen with coordination number = 1
* sp2 nitrogen with coordination number <= 2 
* sp3 nitrogen with coordination number <= 3
* non-aromatic sulfur with coordination number <= 3 

When calculating Nof_HBA property for a molecule there is an option either count number of heavy atoms satisfying one of the conditions above or counting lone pairs on this atoms. (some atoms can shape more than one lone pair)