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Re: [ESPResSo-users] Verlet integrator motion equations

From: Evyatar Arad
Subject: Re: [ESPResSo-users] Verlet integrator motion equations
Date: Mon, 2 Mar 2015 19:37:22 +0200

Hi Florian,

Thanks a detailed answer :)

Have a great week,

On Mar 2, 2015, at 3:18 PM, Florian Weik <address@hidden> wrote:

the integration function is in void src/core/integrate.cpp:214, integrate_vv(int n_steps, int reuse_forces),
the signle steps of the Velocity Verlet are actually in subroutines, which one does what can be seen from the comments.
The forces due to the Langevin thermostat can be found in src/core/thermostat.hpp:162 in inline void friction_thermo_langevin(Particle *p).
The relevant lines are starting at L292. By default we use flat noise and not Gaussian distributed.  We use the classical RAN1 PRNG,
cf. Press, W.H. and S.A. Teukolsky, 1992; Portable Random Number Generators, implemented in src/core/random.hpp:81 for long integers, which
is converted to a double in the same file in the function d_random.


On Mon, Mar 2, 2015 at 1:27 PM, Evyatar Arad <address@hidden> wrote:

I am running NVT simulations with the Langevin thermostat. 

I would like to know where in the code are the Verlet-like equations of motion (namely, including friction and noise) for the new position and velocity of the particles. 

Lastly, I would also appreciate it if you tell me which Gaussian random number generator is used.

Once again, thanks in advance.

Florian Weik, Dipl.-Phys.,
Institut für Computerphysik, Allmandring 3, D-70569 Stuttgart
Phone: +49-711-685-67703
Public Key 0x0562F11D Fingerprint 3294 6360 EC93 37A3 BD40  F597 0BAD 3AF8 0562 F11D

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