bugfixes for pair/hbond/dreiding styles

I've been struggling with really bad dynamics when using
hbond/dreiding/morse for a while, and I think I found the source:

1) There is a bug in pair_style hbond/dreiding/morse which
accidentally erases the angular component of the force. I attached an
animated gif I made which shows the problem
(dreiding_morse_beforefix.gif. The hydrogen and donor were
immobilized during the simulation.) The new version of
pair_hbond_dreiding_morse.cpp (attached) restores energy conservation.
(If fix shake is used to constrain the donor-H bond, it should be
possible to use timesteps in the range of several fs.)

2) I also caught a very minor bug in the "coeff()" member function in
both pair_hbond_dreiding_morse.cpp and pair_hbond_dreiding_lj.cpp

All effected lines are flagged with //<-- BUGFIX 2012-11-14

3) I have some corrections to the documentation for these pair styles
which I'll send later.


pair_hbond_dreiding_morse.cpp (13.4 KB)

pair_hbond_dreiding_lj.cpp (16 KB)



Sounds good - I'll let Tod take a look and comment.



Incidentally (you know this is coming), the bug in dihedral_class2.cpp
is equally serious. I actually know other random people who use that
dihedral style. We need to get that bug patched. Let me know if you
want me to send you the patch again.



I never heard a definitive answer from my class2 "expert".
I'll nag him again ...