Subdiscipline of theoretical physics which consists in the study of physics problems using numerical algorithms. PLEASE NOTE that questions about computational methods and/or programming are OFF-TOPIC on Physics.SE.
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11 views
Spring damper model does not work very well [migrated]
I'm trying to model a spring damper system from a tutorial that I've found on this site.
If I use the exact same parameters as the ones in the tutorial the system is not stable. I've downloaded the ...
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0answers
28 views
Energy Conservation [migrated]
I'm working on a time integration scheme for my research. As a result I have come across an interesting phenomena. Somehow, the total energy of the scheme oscillates. At any given time the total ...
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6 views
Finite Element, NASTRAN, how to print the differential stiffness matrix in .f06 output file [migrated]
We are working on an optimization problem in which we can approximate the eigenvalue calculation by assuming a constant eigenvector, using the formula:
$$
...
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1answer
80 views
Initial position and velocity of rocket to escape earth's gravity
I'm trying to numerically simulate a spacecraft trajectory between earth and mars. I already wrote the solar system model where the sun is at the origin of the x,y,z plane Earth and Mars are orbiting ...
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12 views
Calculation of translational free energy in condensed phase
For gases, the reference volume in molecular calculations is usually understood to be 24.5 L whereas in solution, the reference volume usually is considered to be 1 L.
The free energy corrections ...
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1answer
42 views
Computational Fluid Dynamics methods
I have read some articles about the finite difference method on a cartesian orthogonal grid. I understand how it works when Dirichlet boundary conditions are used, or when Neumann boundary conditions ...
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16 views
Implementing Explicit formulation of 1D wave equation in Matlab #FiniteElements #FiniteDifferences [migrated]
so the theory is straight forward.
we have:
$\frac{d^2U}{(\Delta t)^2}=c^2 \frac{d^2U}{(\Delta x)^2}$
discretizing it gives:
$\frac{U(i+1,j)- 2U(i,j) + U(i-1,j)}{(\Delta t)^2} = c^2 ...
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1answer
54 views
Deriving the change in the Helmholtz free energy in the context of the free energy perturbation method
I am reading Free Energy Calculations: Theory and Applications in Chemistry and Biology by Chipot and Pohorille. At the beginning of the text (page 19, for example), the authors define the Helmholtz ...
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1answer
76 views
What states are satisfying an entropic area law and why do they satisfy it? More specificly why do matrix product states satisfy it?
I am currently reading some papers concerning the question why the density matrix renormalization group (DMRG) method is working well for simulating one dimensional systems and bad for higher ...
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0answers
30 views
Trotter splitting and entanglement entropy
I have heard that a numerical solution to the Schrodinger equation using the Trotter splitting formula for a many-body Hamiltonian can cause an artificial increase in the entanglement entropy. I was ...
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1answer
88 views
How to determine predicted CP violation for a given SUSY point?
I'm currently studying at the spectra of some supersymmetric models, and would like to know whether the parameter points I'm looking at are ruled out due to excessive CP violation.
I am using SPheno, ...
3
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1answer
107 views
Diifference between real time propagation and imaginary time propagation?
Suppose I want to solve Nonlinear Schrodinger equation using imaginary time propagation to get the ground state solution. I choose $t = - i t$, and then solve the equation using split step Crank ...
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73 views
2D quantum well energy spectrum (analytical vs numerical)
I am trying to understand the energy spectrum difference between the analytical and the approximated solution for a quantum well.
The particle is inside a box with domain $\Omega=(0,0)$X$(1,1)$. For ...
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1answer
89 views
reversible cellular automata
Let's suppose a cellular automaton has a value $b(r,t)$ belongs to $Q$ at site $r$ and time $t$, where $Q$ is the set of possible states at each site. Let $N(r, t)$ be the values of the states of all ...
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0answers
62 views
What libraries are available for solving problems at the college physics level? [closed]
Are there any libraries available for solving problems at the level of college physics?
In particular, I'm interested in libraries for general purpose programming languages that can calculate results ...
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2answers
144 views
Difference between Monte Carlo and Quantum Monte Carlo methods?
What are the differences between Classical Monte Carlo methods and Quantum Monte Carlo methods in condensed matter physics? If one want to study strongly correlated systems with Quantum Monte Carlo ...
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0answers
78 views
Difference between a Fixed Point and a Limit Point in implementations of the Renormalization Group (RNG) in Large Eddy Simulation (LES) model
In the introduction of this paper, it is explained that and how the application of a dynamic subrid scale model for turbulence into a large eddy simulation (LES) model corresponds to doing one ...
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1answer
47 views
The number of mean free paths which a particle traverses is independent of the material traversed
This is a manual from a Monte Carlo physics manual:
Computing the occurrence of a process
Can anyone tell me why the number of mean free paths of a particle is independent of the material which it ...
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1answer
187 views
Industry application of computational quantum mechanics?
I was wondering if anybody knew of an industry application of computational quantum mechanics. For example, the efficient placement of circuit elements on a PCB is in part motivated by classical FDTD ...
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0answers
45 views
numerical investigation of stability [closed]
I am trying to find the required specifications of an paul RF trap, in which a proton can be confined.(trap dimensions,voltage frequency and amplitude used, etc). I have to solve the equations of ...
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0answers
112 views
Physics problems requiring numerical solutions to polynomial systems? [closed]
This is a very general/open-ended question.
I wonder if numerical solutions to large scale system of polynomial equations (in many variables) are used in physics at all. I am looking for some good ...
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2answers
86 views
How can one determine at which distance the Lennard-Jones potential reaches a given value?
My question is fairly simple, but I do need clarification on how to get the inverse of the Lennard-Jones potential V(x).
I am working with the following expression:
$$
V(x) = e\times[(R/x)^{12} ...
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1answer
79 views
Magnetic field of permanent magnet [closed]
Hi I am looking for some code to (computationally) calculate the magnetic field of a rectangular permanent magnet in 3D space. Preferably I could edit it to add in my own dimensions. Does anyone know ...
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1answer
242 views
Lennard Jones liquid vapour phase transition
I am trying to generate a phase diagram of pressure versus temperature in a NPT ensemble using molecular dynamics method. I am using the Lennard Jones potential with 108 particles and Berendsen ...
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1answer
83 views
Parameter determining argon phase
Currently I am working a molecular simulation to determine phases of an argon NPT ensemble using Lennard Jones potential. Mainly I use the radial distribution function to determine solid, liquid, or ...
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1answer
81 views
Mutual Interaction of $N$-Particles in a Cartesian Plane
I am making a simulation of $N$-Particles in a cartesian plane and need help with understanding the basics.
At anytime, in my particle system, I will have $N$ number of particles. I am treating the ...
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1answer
107 views
Using the monte carlo method to compute the magnetic field of a curent carrying loop
I have written a program in cpp that computes the magnetic field at a point from a current carrying loop. It uses the biot savart law and the monte carlo technique to carry out the integral. The ...
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1answer
88 views
Strange Behavior in Spring Computer Model
To learn more about oscillatory motion which I am learning about in my high school physics class, I have created a computer model of a damped spring where the damping force is proportional to ...
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1answer
168 views
Help: 3D visualization of magnetic field around moving point charge
The diagrams I'm able to find online only show the concentric field lines in the particle's plane, perpendicular to the motion, which of course generalizes to the cylindrical shape around a conductor. ...
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2answers
128 views
Computational Science involve programming? [closed]
I read what is computational science in Wikipedia but the explanation and understanding are not very clear.
So, I could you please give a simple example computational science project and what all ...
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4answers
163 views
Computer Science Modeling of Physical World
I am curious what efforts have been made to date to define virtual computer worlds based on the physics we know in the real world?
I think it would be awesome to say start off with an atom defining ...
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2answers
153 views
Where does Computer Science background students fit in Theoretical Physics [closed]
I am basically an Electronics student - background in computer science (that's where I want to work). I applied for an internship in USA in a research institute where the group is focused in ...
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2answers
132 views
numerical formulation of Dirac equation plus electromagnetic field
I have the following equations describing the electron field in a (classic) electromagnetic field:
$$ c\left(\alpha _i\right.{\cdot (P - q(A + A_b) + \beta mc) \psi = E \psi } $$
where $A_b$ is ...
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3answers
223 views
Can a wavefunction be solved to any arbitrary precision, given enough computer time?
I learned that the wavefunction for the hydrogen atom can be solved analytically (we did the derivation in class), but that for more complicated atoms it is "impossible" to solve and that only ...
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2answers
215 views
Can I use imaginary time propagation for many-body problems?
There are various ways to numerically find the ground state energy and wavefunction of a many-body Hamiltonian. You can diagonalize the Hamiltonian and pick out the lowest eigenstate, or you use ...
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75 views
Coupled decay behavior? [closed]
I solved the following "coupled" ODE numerically, whit forward Euler scheme:
$$
\frac{\text{d}N_a}{\text{d}t} = -\frac{N_a}{\tau_a}
$$
$$
\frac{\text{d}N_b}{\text{d}t} = ...
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2answers
137 views
Why are Markov chains better than naive algorithm for Random picking?
I have a question about the problem of coming up with a random distribution of non-overlapping coins in a given two dimensional space. I don't understand why using the random sequential adsorption ...
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3answers
336 views
Calculate kinematics of body movement from the set of spatial coordinates
Short intro
I have a set of 3D (x,y,z) spatial coordinates of arm movement obtained using motion capture system. The example set of such coordinates looks like this (rounded up):
...
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54 views
Is it possible to use the properties of quantum mechnics to develop a computer that develop mathmatical theory? [closed]
Is it possible to use the properties of quantum mechnics to develop a computer that develop mathmatical theory?
I want some reference please, because i want to get into very detailed.
Thanks in ...
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2answers
431 views
How do I integrate the Poisson equation to determine the electric potential along a particular direction (e.g., $z$)?
This question is a sequel of sorts to my earlier (resolved) question about a recent paper. In the paper, the authors performed molecular dynamics (MD) simulations of parallel-plate supercapacitors, ...
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1answer
192 views
How is acceleration computed in the leap-frog algorithm in computer simulations of particles?
I am reading the book Computer Simulation of Liquids by Allen and Tildesley (here is another link). On page 80, the authors describe the leap-frog algorithm, which is used extensively in molecular ...
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1answer
262 views
How do you simulate chiral gauge theories on a computer?
David Tong and Lubos Motl have argued that our universe can't possibly be a digital computer simulation because chiral gauge theories can't be discretized, and the Standard Model is a chiral gauge ...
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2answers
122 views
How to decide convergence of the ensemble average in a Monte Carlo process
I am simulating electromagnetic scattering off a rough surface. The usual process is to do a Monte Carlo simulation, which is briefly described as follows.
Generate a randomly rough surface, and ...
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0answers
170 views
fun computational physics projects [closed]
I want to learn how to code in Java and am in need of some cool computational physics projects that would provide motivation to do so. I was wondering if you guys could list some medium-level ...
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2answers
219 views
In condensed matter simulations, how is particle number density computed in practice?
I have been reading a recent paper. In it, the authors performed molecular dynamics (MD) simulations of parallel-plate supercapacitors, in which liquid resides between the parallel-plate electrodes. ...
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3answers
817 views
Why is the canonical ($NVT$) ensemble often used for (classical) molecular dynamics (MD) simulations?
Molecular dynamics (MD) simulation is a common approach to the (classical) many-body problem. It relies on integration of Newton's equations of motion to simulate the trajectories of many (e.g., ...
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3answers
331 views
Adding rotation to internal coordinates
I'm optimizing the geometry of a system composed of several interacting masses (a molecule). The energy of the system depends on the relative position of the masses, and all velocities are zero.
In a ...
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0answers
35 views
bond energies database [closed]
I’m looking for a public database of bond energies of biochemical compounds. Do you know about any?
Otherwise, which is the standard computational methodology to calculate them? Any references would ...
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0answers
142 views
Quantum Compting or DNA computing [closed]
My friend and me are working on DNA computing and on some improvements to it.
Of course, we are working on computing aspects of this branch. So, we have insufficient knowledge about physics and ...
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367 views
Calculating semi-major axis of binary stars from velocity, position and mass
I'm trying to calculate the 'instantaneous' semi-major axis of a binary system with two equal (known) mass stars for an $N$-body simulation. I know their velocities and positions at a given time, but ...
