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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 ...

3
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1answer
24 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 ...
-1
votes
0answers
24 views

How many update between two successive samples in Ising model?

I am simulating 2D and 3D Ising model Using Wolff single cluster algorithm. I want to know how many Monte Carlo steps is needed between two successive samples. I perform 10^6 sampling for 2D Ising ...
1
vote
1answer
50 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 ...
-1
votes
0answers
22 views

Numerically solving a system of parabolic PDEs and 1st order ODEs [migrated]

I'm trying to solve the following system of differential equations numerically. What are the available finite difference approaches and matlab solvers to solve such a system? Other approaches to solve ...
-1
votes
0answers
14 views

How to visualize my three dimensional experimental data with MATLAB? (STM line cut ) [on hold]

I perform STM experiment, and I have a lot of data to deal with. It's a line cut, that is a three dimensional data: distance, bias and DOS. I wanna visualize the data as a 3D map with MATLAB, how ...
0
votes
1answer
46 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
37 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
25 views

COMSOL magnetic field time dependent [on hold]

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
42 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
116 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
47 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
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0answers
18 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 ...
0
votes
1answer
21 views

Can you use HLvL scheme to solve these quations?

I successfully used HLvL scheme (https://epubs.siam.org/doi/10.1137/1025002) to numerically solve set of equations of this type: $\frac{\partial u}{\partial t} + \frac{\partial f(u)}{\partial x} = 0$...
1
vote
1answer
36 views

How to improve this simple Brownian motion simulation by adding viscosity?

I've written a 0th order Brownian motion simulator to envision how a particle of smoke might appear to move under a microscope. There will be missing $\sqrt{2}$'s and $\frac{\pi}{2}$'s since I haven'...
0
votes
0answers
7 views

Likelihood - Difference between deducing original signal and deducing parameters of PSF (Point Spread Function) [migrated]

I make confusions in the using of Maximum Likelihood to find (approximately) the original signal knowing the data observed and the using of Maximum Likelihood to find estimations of parameters of the ...
3
votes
1answer
108 views

The acceleration of the particles by finite difference [closed]

I would like to approximate the acceleration of a molecular dynamics system. I'm following an online tutorial to solve a set of equations for molecular dynamics. I can use $F=ma$ to calculate the ...
1
vote
0answers
54 views

Numerically solving a partial differential equation [migrated]

I am trying to numerically solve the following PDE, $$\frac{\partial u^A}{\partial t} = c_1\frac{\partial^2 u^A}{\partial^2x} \,,$$ where $c_1$ is a constant. The above can be discretized using the ...
1
vote
1answer
35 views

Hamiltonian for a 1D spin chain

I am trying to implement the Lanczos algorithm to tridiagonalize the Hamiltonian for a 1D spin chain of length $L$, but I am unable to decipher from my professor's notes (here's a link), what the ...
0
votes
0answers
29 views

What is fundamental reason behind the 'Slowly Varying Envelope Approximation' while solving Electromagnetic problems?

I wonder how much do we deviate from the exact scenario when this approximation is applied? Can anyone help me out by giving a physical interpretation of this approximation?
3
votes
1answer
95 views

How to numerically solve the Schrodinger equation for the hydrogen atom?

From the analytical solution for the hydrogen atom I remember that the energies were obtained by boundary conditions and then the energy depends on n*n in which n is interpreted as different energy ...
1
vote
1answer
77 views

Why are simulations like Monte Carlo or Metropolis studied for Ising Models when 1d and 2d case have analytical solutions?

I know that absolute analytical solutions exist for the 1d and 2d case but need some intuition as to why these simulation algorithms are used and how do we benefit from them ?
12
votes
3answers
1k views

Does quantum mechanics allow you to simulate chemical reactions in software?

I'm a software developer interested in learning quantum mechanics to simulate chemistry. I know it's a very difficult topic, so I consider it a long term "someday/maybe" goal, and I’m not sure it's ...
0
votes
0answers
24 views

How to decide step size(sigma value) in MCMC routine related Cosmological Parameter estimation?

I am running a modified Lambda-CDM in MCMC routine using Montepython and CLASS code, with aim to extract parameter values from Planck data. In addition to the original 10-15 parameters for Planck ...
1
vote
0answers
29 views

What type of potential is suitable for ion bombardment in Molecular Dynamics?

I would like to study ion bombardment on targets with molecular dynamics, especially on oxides. So far I ran conclusive tests with Lennard-Jones potentials, but I would like to obtain better ...
1
vote
1answer
97 views

Fourier transform of a wavefunction

After solving the Schrodinger equation numerically by finite difference method for some potential. I can plot the wavefunction with the distance from nucleus and I get the right theoretical shape. ...
0
votes
1answer
17 views

Integrating a function defined in Matsubara frequencies

I am writing a code for the numerical evaluation of susceptibilities. The formalism is explicitly written on the Matsubara axis (fermionic case) and in the heart of the procedure lie multiple ...
0
votes
0answers
12 views

Simulation of a rotor with a shroud

I am doing a simulation of a rotor with a shroud to know about the effects of the shroud to the aerodynamcis performance of the rotor. I am using Fluent to do this project. For me, there are two ways ...
0
votes
0answers
27 views

Non-hermitian hamilton matrix in velocity-gauge?

When using the velocity gauge $\mathbf{\hat{p}} \rightarrow \mathbf{\hat{p}} + \mathbf{A}(t)$ with the dipole approximation $\nabla\cdot\mathbf{A}=0$ to describe light-matter interaction, the ...
1
vote
0answers
52 views

Ice blocks melting outdoors [closed]

I have a question, that is not related to anything academic. We are planing a festival in winter, that will have some stage set up of ice blocks. There will be several big rectangular prisims of ice, ...
4
votes
2answers
260 views

How can I include variable particle number in a Brownian dynamics simulation?

I programmed a Brownian dynamics simulation in two dimensions. (Coarse-grained proteins on surfaces with interaction potentials i.e. patchy particles.) Now I want to allow particles to leave or enter ...
0
votes
0answers
14 views

Response matrix in unfolding algorithm in high energy physics

I am studying unfolding algorithms developed in high energy physics. The algorithms starts by the discrete version Fredholm integral equation. There are many methods to produce discrete version of ...
2
votes
2answers
85 views

How does particle physics use deep neural networks to find particles?

Does anyone use deep learning: RNN, CNN or any other architecture of deep neural networks to asses the standard model or to detect new or unseen particles? What's the status these days in this ...
1
vote
0answers
43 views

How to perform a convergence test of Runge-Kutta numerical integration [closed]

I've come across multiple assignments now where I am to calculate trajectories, orbits etc. using the Runge-Kutta 4th order method. However, each time I am also asked to perform the correct ...
1
vote
0answers
50 views

Self-modifying Hamiltonians (Lagrangians) and emerging intelligence? [closed]

Are there dynamical physical systems that are governed by self-modifying Hamiltonians (Lagrangians), i.e. Hamiltonians (Lagrangians) determine not only the next point in phase space, but also the form ...
1
vote
2answers
68 views

Estimate of the period of noisy “event counting” data

I have a set of experimental data, which come from a periodical event. More specifically, these are detections from a single photon detector, so there is no intensity, I only have the timestamps of ...
0
votes
0answers
81 views

Inverted double pendulum - difference between hand calculation and Simulink/Simscape

I have following problem - I'm using Lagrange's equations to describe inverted double pendulum with torsion spring at each of two joints. I solved obtained ODE in Matlab, receiving functions $\Phi_1(t)...
24
votes
9answers
4k views

How does a particle know how to behave? [duplicate]

How does a particle know it should behave in such and such manner? As a person, I can set mass is so and so, charge is so and so - then set up equation to solve its equation of motion but who ...
0
votes
0answers
30 views

Is simulating the interaction of multiple particles possible in $0$ spacelike and $3$ timelike dimensions?

In multiple time like dimensions it is possible for particles to effect it's own past, and two particles can both be effected by each others future. I tried to simulate the interaction of multiple ...
0
votes
0answers
29 views

How do I convert raw Electric field wave data into a frequency spectrum?

My collaborator performed some FDTD simulations for me and sent me the E-field information by mistake instead of the frequency spectrum collected at a certain point. What is the best way to convert ...
0
votes
0answers
28 views

Within the block matrix algorithms for layered media, is the coupling of the s and p polarizations necessary for linear, homogeneous, isotropic media?

I was wondering this because I have been trying to implement interference effects in a 3D modeling program which can be very limiting. Basically, it would be best if I could separate the calculations ...
1
vote
0answers
20 views

Pairwise additivity of numerical potentials

Surely this is a trivial problem, but I'm very much confused on how to approach so please bear with me. Say I have a two-dimensional evenly-spaced 16x16 grid centered at the point (x1,y1). I also ...
2
votes
0answers
29 views

Looknig for resources on finding periodic orbit and stability on multidimensional Hamiltonian systems

I am looking for resources (books, papers, algorithms, codes) that explicitly explain the computation and analysis (using the monodromy matrix) of periodic orbits of multidimensional Hamiltonian ...
0
votes
1answer
37 views

Computational limits of the universe?

Is our theoretical data storage size and processing bounded by physical laws? I would assume computation is, but is information storage limited by entropy or the physical volume of the universe?
2
votes
0answers
45 views

Barkana & Loeb's Virial Radius Plot [closed]

Recently I have been trying to teach myself the basics of modern cosmology. To do so I have been using Barkana & Loeb. I've been working my way through and come to virial radius. They give the ...
0
votes
0answers
40 views

How accurate will a simulation of the double pendulum using the RK4 method be?

I ask because I have recently been reading about issues with the RK4 method in problems that require the conservation of the Hamiltonian. Since RK4 is not a symplectic integrator, I assume that the ...
0
votes
0answers
26 views

Heat capacity of LJ fluid vs Ideal gas

I am making my first MD simulation about a Lennard-Jones fluid: an Argon system made up of $500$ particles. I need to write e report and answer to some questions. I computed the heat capacity of the ...
0
votes
0answers
36 views

Are strings capable of information processing? If so would string computers be more powerful than quantum computers?

A deterministic computer is weaker than quantum computer at least quadratically for (almost) all kinds of tasks. This is proved and the difference arises from Grover's search algorithm, which allows ...
3
votes
1answer
99 views

How to “build” a proton

Sabine Hossenfelder in her column The End of Theoretical Physics As We Know It made the following statement: For example, we have a perfectly fine theory that describes the elementary particles ...
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0answers
35 views

Spatiotemporal patterns around continuous phase transitions

Consider the Ising model near criticality, a clear spatiotemporal pattern emerges, with scale free clusters shifting around in space, over time. Similar behaviour can be observed in the voter model, ...
-1
votes
1answer
47 views

Help with 2nd Order Coupled ODEs [closed]

I am trying to solve a 2nd Order Coupled ODE for A "Looping Pendulum" numerically with MATLAB. Can anyone please recommend how? (which ODE solver to use) Thanks!