How to reduce enthalpy in an NPH ensemble?

Dear all,
In order to catch the phase transition in a supercooled Si liquid, I have to simulate the system in an NPH ensemble, slowly reduce the enthalpy, or extract kinetic energy from the system, to decouple the system from the thermostat and detect the release of latent heat. But how to reduce the enthalpy or extract kinetic energy in an NPH ensemble ?

Sincerely
Bo Shen

Hi Bo,

I don't have answers for you but questions. Please feel free to
correct me if I am wrong.

1). People study phase transitions with microcanonical (NVE) or
canonical (NVT) ensembles, their inequivalence, and equivalence under
some conditions. What is the reason that you *have* to study phase
transition with an NPH ensemble?

2). If an NPH ensemble is inevitable, does it not sound
counter-intuitive that one wishes to change enthalpy of an isenthalpic
system?

Cheers,
Ray

Bo,
You could do a series of consecutive NPH runs where you artificially
reduce the temperature/enthalpy by rescaling the atomic velocities.
The paper below gives details in its method section. It looks exactly
what you are trying to do (reproduce?)
doi:10.1038/nmat994
Nature Materials 2, 739 - 743 (2003)
Yet, notice that H will be conserved on each of the individual runs as expected.

Hi Bo,

I don't have answers for you but questions. Please feel free to
correct me if I am wrong.

1). People study phase transitions with microcanonical (NVE) or
canonical (NVT) ensembles, their inequivalence, and equivalence under
some conditions. What is the reason that you *have* to study phase
transition with an NPH ensemble?

Ray, I believe this was Bo literally using the definition of the enthalpy.
If:
\delta H = T \delta S + V \delta P

at constant P the changes in enthalpy equal the heat that
enters/leaves the system thus the latent heat.

2). If an NPH ensemble is inevitable, does it not sound
counter-intuitive that one wishes to change enthalpy of an isenthalpic
system?

True. He wants to change it but needs several independent systems to do it so.
Carlos