Issue Regarding q6 module

[ron ban]

Hi everyone,

I had 2 queries using the Q6 module in 2.10 and 2.8 versions

1. I had been using the Q6 module in plumed 2.10 and a lot of times it just gives nan as output. But when I use plumed 2.8 version for the same .gro I get some value instead of nan. This happens with a variety of systems not for a specific system. Most of the times Q6 vmean just returns a nan value.

2. For this I had been using the 2.8 version to do the simulations but it is very slow compared to the 2.10 version. I have been trying to restraint q6 at a certain value by using a restraining force and the simulations take around 4ns/day for a system of 8100 atoms ( calculate q6 of around 2000 oxygen atoms in each 10 steps) using the 2.10 version (which works for this specific system) but gives a speed of around 0.16ns/day for the 2.8 version running in 48 cores. 

Yours sincerely 

Ron