[gmx-users] Annealing doesn't work with Andersen thermostat?

[William Welch]

Hi,
I am doing some simulations on simple Lennard-Jones spheres and course
grained hydrocarbon models. I have been using the annealing utility
successfully until I switched from the V-rescale thermostat to the Andersen
thermostat. When I use the Andersen thermostat, the system gets to the
first temperature and then stays there. This does not happen if I switch to
a different thermostat. My guess is that Andersen not available with
annealing, at least in the version I'm using (4.6) , however I have not
been able to find any reference to that online or in the mailing list. Here
is one of the mdp files that produced a simulation that did not work. .

 title               =  8pore
integrator          =  md-vv
dt                  =  0.003    ; ps !
nsteps              =  2500000  ; total 7500 ps.
nstcomm             =  1
nstxout             =  2000
nstvout             =  2000
nstfout             =  0
nstlog              =  100
nstenergy           =  1
nstlist             =  10
ns_type             =  grid
rlist               =  1.5
rcoulomb            =  1.5
rvdw                =  1.5
; Berendsen temperature coupling is on in two groups
Tcoupl              =  Andersen
tc-grps             =  LJ BL
tau_t               =  0.1 0.1
ref_t               =  230 230
; Energy monitoring
energygrps           =  LJ BL
energygrp-excl       =  BL BL
freezegrps           =  BL
freezedim            =  Y Y Y
; Isotropic pressure coupling is now on
;Pcoupl              = berendsen
;Pcoupltype          = isotropic
;tau_p               =  0.5
;compressibility     =  4.5e-5
;ref_p               =  1.0
annealing            = single single
annealing-npoints    = 20 20
annealing-time       = 0 200 400 800 1200 1600 2000 2400 2800 3200 3600
4000 4400 4800 5200 5600 6000 6400 6800 7200  0 200 400 800 1200 1600 2000
2400 2800 3200 3600 4000 4400 4800 5200 5600 6000 6400 6800 7200
annealing-temp       = 100 200 230 240 250 260 270 280 290 300 310 320 330
340 350 360 370 380 390 400 100 200 230 240 250 260 270 280 290 300 310 320
330 340 350 360 370 380 390 400
;Generate velocites is off at 300 K.
gen_vel             =  yes
gen_temp            =  230.0
;gen_seed           =  173529

Velocities are generated at 230 (which is kind of strange, but changing
that doesn't do anything) and the system cools to 100K and then stays
there. The output in the md.log file shows that the correct ref_t is being
read, but the actual temperature of the system does not increase. The same
input using the md integrator and the V-rescaling thermostat does what it's
supposed to.
Will