[lammps-users] What is the Liouville operator in NPT (Nose-Hoover scheme)

Dear all,

I’m interested in using LAMMPS2001(fortran)to perform NPT (Nose-Hoover scheme,isotropoic volume dilation)in polystyrene with no charges present in my model.
I have 5 questions:
1)What is the total Liouville operator tha corresponds to the NPT(Nose-Hoover), as this implemented in LAMMPS 2001(Fortran)?
2)Can you tell me how the total operator is being separated and factorized in LAMMPS 2001(Fortran)?
3)What are the quantities :
f_eta, eta, eta_dot,omega,omega_dot, f_omega (in ensemble.f)?
4)Which is the conserved quantity, the “hamiltonian”, of the system, in terms of LAMMPS’s variables (NPT(Nose-Hoover))?
5)Can you suggest me a reference (i.e. a paper ) where i can find the NPT(Nose-Hoover) scheme (Liouville operator,separation and factorization) that is performed in LAMMPS2001(Fortran)?If anyone suggests me one please tell me in which quantities in that reference do the above variables correspond:
f_eta, eta, eta_dot,omega,omega_dot, f_omega.

Thanks for your attention!
Dimitris Tsalikis

The NPT in LAMMPS 2001 is nearly the same as in the current LAMMPS,
documented on this page:


The relevant paper is

Melchionna, S ; CICCOTTI, G ; HOLIAN, BL
Molecular Physics; 20 Feb. 1993; vol.78, no.3, p.533-44
Hoover NPT dynamics for systems varying in shape and size.

To answer your detailed questions, you’ll need to look at the paper and dig
into the code: ensemble.f in LAMMPS 2001 and fix_npt.cpp in the
current LAMMPS.