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Quantum Mechanics Simulation

Started by June 09, 2002 10:49 PM
10 comments, last by bobman312 22 years, 8 months ago
quote:
Original post by bobman312
As a second side note to Tinkin: I was informed by an advisor on Nuclear Physics that to simulate such stuff is inherently exponential, so it would take 2^100 ''size'' locations to simulate all possible reactions. Even if it is possible to completely encode a single interaction by a single bit (that''s a pretty impressive feat!), it would still take 10^20 gigabytes of hard drive space. I''m going to cut it down to 30 atoms instead and see what happens.


I don''t really know the subject matter here, but I do know aerodynamics/CFD and the like, which can have similar (but much less daunting) memory issues. The way we deal with this type of situation is to model only the most important relationships (reactions in your case). Its like a partitioning problem in a way. For example, you can have 100 atoms, but only model reactions of each atom with up to, say, 5 or 10 nearest neighbors .... I have no real idea if this make sense for quantum mechanics!



Graham Rhodes
Senior Scientist
Applied Research Associates, Inc.
Graham Rhodes Moderator, Math & Physics forum @ gamedev.net
quote:
Original post by Anonymous Poster
How arrogant!!!


Perhaps you should read the question and the answer again. The question was not asking HOW to do something, but whether anyone knew how to do it. I certainly know that it is possible - since I have some understanding of the problem and the solution method - and I have a close friend that has done it (as his Masters thesis) in the field of Quantum Optics: simulating atoms captured in the potential field created by interacting lasers.

quote:
Original post by bobman312
As a side note to Timkin: I''m pretty sure you need the shape in the first place to define the potential.



Well obviously you are going to define a potential that gives the problem a spatial constraint of a 3D cube... I think that I didn''t explain my point properly. Sorry. What I meant was that you define the constraint in terms of the potential function, rather than in terms of spatial constraints that equate to a cube.


quote:
Original post by bobman312
As a second side note to Tinkin: I was informed by an advisor on Nuclear Physics that to simulate such stuff is inherently exponential, so it would take 2^100 ''size'' locations to simulate all possible reactions.



If you wanted to solve for the interaction of all particles with each other exactly, then yes the complexity of the task is exponential in the number of objects. It''s the same problem faced in performing exact probabilistic inference (it''s exponential in the number of variables). In fact, you have the exact same problem, since the problem you are tring to solve is to find the wave function for 100 objects that are all interacting with strengths dependant on their state.

Your question was whether this could be done efficiently and the answer is yes, in so far as ''efficiently'' implies an approximation to the exact answer. You should consider using a Quantum Monte Carlo Method (the less efficient way) or the Masters Equation (a more efficient way) for simulating state transitions in discrete systems.

The Masters equation is a simple case of the differential Chapman-Kolmogorov equation, of which another simple case is the Fokker-Planck equation (which governs all drift-diffusion processes). The Fokker-Planck equation can be transformed into Schrodinger''s Equation, since they model the same thing.

If you want a reference, try looking up:

R.E.Sholten, T.J.O''Kane, T.R.Mackin, T.A.Hunt and P.M.Farrell,
Aust. J. Phys., 52, pp493-514 (1999) ''Calculating trajectories for atoms in near resonant light fields''.

Good luck,

Timkin

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