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Questions tagged [computational-physics]

Questions with this tag should be about computational physics, which is the study of physical situations with the use of software (commercial or in-house). Please note that details of writing and/or debugging code is OFF-TOPIC and should be asked at either Computational Science, Code Review or Stack Overflow.

2
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1answer
31 views

What is this secondary transition in the simulation of the Ising model?

Here, the horizontal axis is the strength of the ambient magnetic field. The Hamiltonian I used is $$H = -h\sum_i \sigma_i - J\sum_{\langle i \, j \rangle}\sigma_i\sigma_j.$$ The horizontal axis is $h$...
1
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0answers
66 views

Fraunhofer diffraction problem in Python: How to interpret discrete Fourier transform (DFT) spectrum?

I have a periodic phase grating consisting of lenslets along the x-direction, invariant in y. I want to use python to calculate the far-field (Fraunhofer) diffraction pattern that one gets when ...
1
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0answers
29 views

Simulating Earth's Atmosphere [closed]

Is there any general purpose open source software currently available that can simulate Earth's atmosphere?
0
votes
0answers
25 views

DMRG for Heisenberg spin chain [closed]

I am learning DMRG. I am writing a DMRG code of Heisenberg chain, which has following Hamiltonian $$H=\sum_i S_i\cdot S_{i+1}$$ The algorithm for infinite DMRG is following: Build left and right ...
-1
votes
1answer
41 views

Mimicking the behavior of a current loop using a finite number of infinitely small sources [on hold]

I am attempting to model the field produced by either a loop of current, or a magnetic moment. In either case I am assuming that the distances I care about are sufficiently far from the source to not ...
2
votes
1answer
46 views

Scaling Problem with Variational Method

$\def\braket#1{\langle#1\rangle}$ I am attempting to solve a particular Hamiltonian by variational method. The wavefunction that I have selected is as follows: $$ \Psi = Ne^{\frac{-kr}{2}}\sum_{i=0}...
1
vote
1answer
27 views

Vector Poisson Equation for a symmetrical geometry

I was recently doing some simulations involving the vector Poisson equation and symmetrical geometries with respect to one plane. My question is basically if the computations involved can be reduced ...
-1
votes
0answers
57 views

Could uncomputable processes and things exist in a spin-networks-based universe? Even observable uncomputable processes and things?

Roger Penrose proposed a series of networks from which, fundamentally, space-time would emerge, called spin networks (https://en.wikipedia.org/wiki/Spin_network) Also, in this paper https://...
1
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0answers
51 views

Wolff cluster update in Monte Carlo simulation - at critical temperature [closed]

A general question to the Monte Carlo experts. When I use Wolff algorithm for global updates, say for Ising 2d, I always flip at least one spin (the initial random spin in the cluster). So, near the ...
0
votes
1answer
50 views

How can the analytical solution of the diffusion equation be used for a series of $N$ positions?

Given the exact solution to the diffusion equation: $$C(x,t) = \frac{1}{\sqrt{4 \pi D t}} \exp\left[-\frac{x^2}{4 D t}\right]$$ I am unsure as how it can be applied to a 1D series, as this equation ...
-1
votes
1answer
36 views

Non-linear optics - solve differential equations coupled with the finite difference method [closed]

I have these three differential equations in which I need to solve numerically: $$ \frac{dn_0}{dt}= -n_0(t)W_{01}(t) + n_1(t)K_{10} $$ $$ \frac{dn_1}{dt}= -n_1(t)W_{12}(t) - n_1(t)K_{10} + n_2(t)K_{...
0
votes
0answers
15 views

Computational solution of exponential decaying wavefunction tail

As I am going through some (quite simple) computational physics exercices I have a question concerning one exercise that involves solving the radial Schrodinger equation. This is done with the ...
-1
votes
1answer
56 views

Numerical approximation of the wavefunction in a delta-potential [closed]

I am trying to approximate the wavefunction of a particle in a delta potential $U(x) = -U_0 \delta(x)$ with $V_0 \gt 0$. I am using the following formula to calculate the wavefunction: $\psi(x+\Delta ...
0
votes
0answers
36 views

Finding ground state energy using numerical real space renormalization group

I want to find ground state energy (as well as wavefunction) for spinless $tV$ model using Real-Space Renormalization Group (RSRG) approximation. The $tV$ model is defined as $$H=H_t+H_{int}=-t\sum_{i=...
5
votes
1answer
73 views

Is there any relation between density matrix renormalization group (DMRG) and renormalization group (RG)?

Probably I am going to receive many down-votes for this post but I really need to ask this question here. I am new to statistical mechanics. I wanted to learn Density Matrix Renormalization Group (...
2
votes
2answers
114 views

How can I explicitly express the Ising Hamiltonian in matrix form?

I am reading this book about numerical methods in physics. It has the following question: Consider the Ising Hamiltonian defined as following $$H=-\sum_ {i=1}^{N-1} \sigma_i^x \sigma_ {i+1} ^x + h ...
-2
votes
1answer
93 views

Putting high symmetry points labels to a band structure plot [closed]

So far I've got this plot using Quantum Espresso. I want to put gamma, X, L, etc labels to the k-path. Quantum Espresso's ouput states the following: ...
10
votes
2answers
276 views

How can one obtain the metric tensor numerically?

I am self-studying General Relativity. Is there a method for obtaining the metric tensor exterior to a specified mass distribution numerically? In the simplest case of a spherical mass this should ...
-1
votes
0answers
35 views

Would uncomputability be a problem for Zuse's thesis?

Konrad Zuse worked in a model that described the universe as a cellular automata. My question is: There are some other authors that say that there are things (for example, processes) that are ...
0
votes
1answer
42 views

Ising magnetization in metropolis

I am working on the Metropolis-Montercarlo algorithm for the square lattice ising 2D. Im running the simulations for a given lattice size, running from low temperature to high temperature, and ...
1
vote
1answer
43 views

Is numerical lattice wavefunction smooth? — graphene tight binding case

I tried to follow exactly Sec. II.K [page 112-113, Hamiltonian after Eq. (113)] of the standard Review of Modern Physics paper on graphene, which is a tight-binding model of a graphene stripe under ...
0
votes
2answers
54 views

Runge Kutta 4 for orbits and Newtonian Mechanics

How can I use the Runge Kutta 4 method to solve orbits of Newtonian Mechanics, with position vector $\mathbf x$, velocity vector $\mathbf v$ and acceleration vector $\mathbf a$? Do I still have to ...
1
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0answers
51 views

Negative Eigenvalues of the Hessian

I am calculating the eigenvalues of the Hessian for a ferromagnetic system. My energy has the zeeman term, a nearest neighbor exchange term, and a dipole-dipole term. I create the hessian where my ...
0
votes
1answer
62 views

Motion of the center of mass of rigid bodies in space

For the classic two body problem, I know that the motion of the center of mass is a straight line (with respect to an inertial frame), provided that the bodies are considered as point particles. Now ...
1
vote
2answers
118 views

Implementing a spherical pendulum

I am trying to implement a spherical pendulum. The Lagrangian (which I haven't fully understood so yet) based on $l$, θ and φ taken from this page result in the equations: \begin{align} \...
2
votes
1answer
38 views

What the difference is between Størmer Verlet and regular Verlet method?

I was wondering what the difference is between the Størmer Verlet method and the regular Verlet method, if there is any.
0
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0answers
31 views

Amplitude of a wave: will it be an overlap of two waves or is there another reason?

For a wave with initial conditions and with a velocity = 1.00 m / s the following graph was obtained: The spatial domain is [0; 50] m and the time domain is [0, 50] s. The wave reaches the boundary ...
1
vote
1answer
86 views

Brownian dynamics simulations in confined geometries [closed]

I am currently trying to implement a 2D Brownian dynamics simulation in confined geometries (corrugated channels, of the form $A\cos(2 \pi x) \ + B\ $ in this case). The concept is to compute the ...
0
votes
1answer
30 views

How do I determine the accuracy of this two-dimensional potential field?

Let's say I want to solve this problem. I know the values on the boundaries and I guess an initial solution on the rectangular grid inside these boundaries, see figure below. Potential=10 on ...
1
vote
0answers
44 views

Collision response with spring physics in RK4

I'm trying to figure out what's in the title. I've gotten regular spring physics working and now I'm trying to do something similar with actual collisions (player character colliding with the ground ...
1
vote
1answer
29 views

Where to find numerical simulations for motion of particles in Schwarzschild geometry?

I have written a simulator of particle motion in the Schwarzschild geometry and I would like to compare it to other peoples' results. Where can I find a paper where they have done numerical ...
1
vote
2answers
91 views

Can I apply the standard Runge Kutta 4th order method to the Langevin Equation?

If I have a Langevin Equation with an external force term (which may be time dependent), is it possible for me to apply the standard 4th order Runge Kutta algortihm to solve it numerically? Edit: I ...
0
votes
1answer
39 views

What is the error propagation in an FFT (Fast Fourier Transform)?

I use an insert FFT graph feature on a program called logger pro. If I have the uncertainty of my input data, can I know what the uncertainty of the FFT computation will be?
2
votes
1answer
54 views

Is quantum computation just an advanced data compression algorithm?

When we are talking about the quantum computation and classical computation, we are saying that quantum computation is exponential faster than the classical one. And that's because the Kronecker ...
8
votes
1answer
110 views

Difficulty of numerically solving Einstein equations

The most recent episode of Sean Carroll's podcast is an interview with Kip Thorne, in which it is stated that until somewhat recently it was unclear that it would ever be possible to simulate the ...
2
votes
1answer
16 views

Can we estimate the coefficient of friction between two objects/materials?

I remember reading that it was impossible to theoretically estimate the coefficient of friction between materials even if their structure was known. The book where I've read this was The Feynman ...
0
votes
1answer
45 views

Importance of analytic solutions to Hamiltonians

Why is it important to attempt to find an analytic solution for any theoretical model? It usually happens that many of the hamiltonians written to model the system may not usually have exact solutions....
0
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0answers
21 views

Tutorial for the quantum jump method

Are there any tutorials that you would recommend for self-learning the quantum jump method or quantum Monte-Carlo. I am not exactly into Quantum Optics, so I would really be interested to see how is ...
2
votes
1answer
40 views

Solar System Position and Velocity data

I'm trying to create an nbody simulator and to test it I'd like some real world data. A good test would be the solar system. I've come across the JPL Horizons software but if cant seem to figure out ...
0
votes
2answers
47 views

How to animate a ball rolling down an incline?

I'm using Lagrangian mechanics to come up with the equations of motion for a ball rolling down an incline. I've come up with the following two equations. $$\begin{alignat}{1} \dot{x} &= \frac{2}{...
2
votes
1answer
52 views

Visually and physically reasonable analytic approximation to the field of a bar magnet

I want to produce publication-quality drawings of the field of a bar magnet, in both the field line representation and as a "sea of arrows." I've found some open-source software that looks like it ...
0
votes
2answers
30 views

Programmatically generate valid density matrices of arbitrary dimension

I would like to generate a random $N\times N$ density matrix for a program. My current technique works for qubits but I suspect there are much more elegant ways. For a single qubit state, I write $\...
1
vote
1answer
95 views

Weird results of Monte Carlo simulation

I'm simulating the 3D Ising Model using the Wolff update algorithm. I am using the Mersenne Twister RNG. When the lattice size is $L = 50$, the specific heat curve looks very weird!! I want to ...
0
votes
1answer
65 views

Implementing a Monte Carlo Simulation for the Gaussian Model

I want to implement a Monte Carlo simulation of the 1D Gaussian Model (the continuous generalisation of the Ising Model). That is the statistical mechanical model with the following Hamiltonian: $$ H ...
4
votes
1answer
45 views

Why is FDTD derived directly from Maxwell's equations instead of the wave equation

I've been wondering why the Finite Difference Time Domain Method is derived directly from Maxwell's equations and not directly from the electromagnetic wave equation (that in theory is also derived ...
1
vote
0answers
47 views

COMSOL magnetic field time dependent [closed]

enter image description here I need to modelling conductor in Comsol 5.3 by MF physics in Time Dependent study Conductor model "Single conductor" in "Coil" feature doesn't work in TD study, and ...
2
votes
1answer
59 views

Solving Schrödinger equation by neural networks - trial function explanation

I'm reading this paper about solving Schrödinger equation using the combination of genetic algorithm and neural networks. But one part confuses me - the author defines his trial function, i.e. the ...
2
votes
0answers
126 views

Computational content of Feynman integral

I am looking for references with rigorous (not just numerical) studies deriving convergence rates of discretized path integrals to their "true" values in some interesting special cases (since the ...
3
votes
1answer
55 views

Laplace's heat equation equilibrium functions

I simulated the Laplace's heat equation on a grid (200x200) with boundary conditions of 0 (a cold source) on the top and left and 1 (of hot source) on the bottom and right. (see gif) I stopped ...
0
votes
0answers
28 views

What is the difference between density functional theory and ab initio molecular dynamics?

I feel like I should know the answer to this question. But in standard implementations of (say) plane-wave DFT in softwares like VASP, the atomic positions are moved based on the Hellman-Feynman ...