[gmx-developers] Two questions about Nose-Hoover chains

[Andrew DeYoung]

Hi,

I am a graduate student and am relatively new, in the last year, to MD
simulations.  If you have time, may I ask you for advice about concepts
related to Nose-Hoover chains?

(1) Do you happen to know of any good review-type articles or tutorials on
the concept of Nose-Hoover chains.  Unfortunately, I am not so strong in
either statistical mechanics or Lagrangian mechanics, so when I read (for
example) the original Nose-Hoover chain papers by Martyna, I get lost very
quickly.

I understand that the basic Nose-Hoover method relies on the introduction of
a heat bath and an associated friction parameter; this friction parameter
modifies the equation of motion (i.e., Newton's equation) by adding an
additional term which contains the momentum of the friction parameter xi and
a mass parameter Q.

I also understand that the basic Nose-Hoover method can be non-ergodic and
to remedy this, Nose-Hoover chains are introduced.  Are Nose-Hoover chains
simply additional friction parameters xi?  Or are they additional
thermostats "chained" to the original Nose-Hoover thermostat?  Can you
recommend any overview reading to help me get the basic conceptual idea?

(2) Why are (multiple) Nose-Hoover chains not implemented in the leap frog
(md) integrator?  This is NOT a criticism; I am just curious if there is any
conceptual idea behind the inability to use chains with the leap frog
algorithm. 

Thank you so very much for your time! 

Andrew DeYoung
Carnegie Mellon University