X value not converging to 1

From: Collier, Angela <acco239_at_g.uky.edu>
Date: Tue, 24 Nov 2015 09:16:29 -0500

I am running GADGET2 and GADGET3 tests with 10K-100K collisionless
particles using physical coordinates. For the initial conditions, I assign
positions to the particles to fit an NFW profile with a Gaussian cutoff, and
either give them v=0 or about 80% of the virial velocities. I run the model
for about 10-15 free fall times (or crossing times) to see how the system
relaxes to the virial equilibrium, i.e., to the virial ratio X=1. When I
run from v=0, the system relaxes to X~1 in about 3-4 free fall times, then
oscillates around this number. When I run from ~80% of the virial
velocities, the system relaxes to X~1.1-1.2 range. The total energy
conserved at the level of ~0.2%. What could be the reason for this strange
value of X?

For general info, the parameters are:
I use 2 nodes with 32 cores
ErrTolIntAccuracy 0.005
ErrTolTheta 0.4
ErrTolForceAcc 0.001
PartAllocFactor 15.0
TreeAllocFactor 0.7
Thank you,
Angela
Received on 2015-11-24 16:11:15