Null "sas" value when performing decomposition of PB results

[Shianine]

Hi, I am running per-residue decomposition based on MM/PBSA results using gmx_MMPBSA. I am curious about the "sas" term in decomposition result. I guess it should be the non-polar part of desolvation contribution. Is that right? Then why the value of this term in decomposition is null? Can this energy term be decomposed? 

[marioe911116]

This is the hardest term to deal with when it comes to decomposition. Most methods are well-suited to calculate total SAS rather than per-residue SAS. I personally haven't gone too much into detail about this, but my guess here will be that the term obtained was not appropriate (e.g. negative area due to the parameters in the method) and then the output is automatically set  to 0