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Questions tagged [computational-physics]

The bridge between theoretical and experimental physics which utilizes numerical analysis, specifically through the use of software, to solve problems in physics. This tag is NOT intended for use in solving problems on paper. 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.

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Diagonalizing the Hamiltonian in plane wave basis to solve the finite square well doesn't work properly

The potential for a finite well is given by $$ \begin{equation} V(x) = \begin{cases} 0,\,&|x|> a\\ -V_0,\,&|x|\leq a \end{cases} \end{equation} $$ I try to determine ...
dao minh duy's user avatar
2 votes
1 answer
78 views
+50

Why doesn't Car-Parrinello molecular dynamics require an SCF calculation?

Reading the various terms of the Lagrangian in Car–Parrinello molecular dynamics, I'm trying to understand why there is not an SCF procedure hidden there. In fact, it seems to me like the second term ...
Chemistry.'s user avatar
1 vote
0 answers
47 views

Numerical Solution of the circular restricted three body problem [closed]

I am trying to numerically solve the differential equations in the planar circular restricted three-body problem. In the rotating frame, the differential equations are given by \begin{equation} \...
Markus Hamre's user avatar
1 vote
0 answers
79 views

Why are quantum-many body problems difficult to solve? [duplicate]

I am a little confused about which classes of interacting many-problems are considered intractable. Suppose I have some tight-binding system with some nearest-neighbor density-density interactions, ...
meer23's user avatar
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2 answers
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Can we catch signals from a cellphone using an external device? [closed]

What if someone stole em waves from our mobile devices to listen to our conversations or get our OTP. Whatever encryptions they have they are just EM waves innit and they cannot be propagated only in ...
Newtron Malayalam's user avatar
2 votes
1 answer
48 views

Accuracy of the Higuera-Cary Particle Pusher

UPDATE: 12 July 2024 This question has been answered. Also, I figured out the problem. One of the papers I was referencing (Ripperda et al.) had a typo, which was leading to the errors. The method is ...
Mohammad Yasir's user avatar
-1 votes
0 answers
41 views

Solving TOV equations that describes neutron stars in modified f(R, T) gravity

Sorry for the long post, tldr at bottom. I'm trying to use standard RK4 code in C/C++ to solve a coupled system of 2 modified TOV equations in f(R,T) gravity and reproduce some of the results of this ...
hidenori's user avatar
1 vote
1 answer
67 views

DMRG for anyons

I want to do some DMRG calculations for anyons. For example, consider the golden chain model for fibonacci anyons. https://arxiv.org/pdf/cond-mat/0612341 I have two anyon types: $1, \tau$. However, ...
Souroy's user avatar
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2 votes
0 answers
54 views

Cosmological numerical computations

I am unsure where to ask this question, whether here or in the Mathematica stackexchange, but either way, I was wondering what are some recommendations for cosmological computations specifically using ...
0 votes
0 answers
41 views

How to Properly Discretize Semiconductor Continuity Equations

I am looking to perform numerical modeling of a MOSFET device and am wanting to better understand how to discretize the semiconductor continuity equations. The semiconductor equations consist of the ...
Schoppe's user avatar
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1 vote
1 answer
69 views

Using Jacobi Method for Solving Full Semiconductor Equations

I am looking to perform modeling of a MOSFET device and have therefore been researching computational methods for how to do so. Quite often when solving the Poisson equation, the reader is pointed to ...
Schoppe's user avatar
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Add pressure gradient to Falkner-Skan (FS) boundary layer (BL) equations and solve numerically for arbitrary $P(x)$

I have read quite a few tutorials / watched several clips on the derivation of the Falkner-Skan boundary layer equations using similarity and then solution using RK solvers such as ...
TriJB's user avatar
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0 votes
0 answers
27 views

Asking advice for numerical implementation of Conservative Finite Difference Method for solving Gross-Pitaveskii equation

I am trying to numerically solve the Gross-Pitaevskii equation for an impurity coupled with a one-dimensional weakly-interacting bosonic bath, given by (in dimensionless units): \begin{align} i \frac{\...
sap7889's user avatar
2 votes
0 answers
29 views

Coordinate transform to account for periodic boundary conditions

I have this nice 2D wave packet that is coherent in both R and K space. I am trying to analyse its dynamics in the presence of a perturbation using semiclassical equations of motion and then compare ...
Abhiram Cherukupalli's user avatar
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0 answers
53 views

Finite Difference Modeling of MOSFET Device

Does anyone know of any references for MOSFET modeling done using the Finite Difference Method that they could point me to? I understand the gist of the operation, namely using Poisson's equation to ...
Schoppe's user avatar
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1 vote
2 answers
98 views

Which higher-order terms require 4th-order integration of quadratically-constrained dynamics?

I was interested in demonstrating the notion of geodesics in constrained motion and prepared the calculation of force-free motion on the unit sphere, following Hertz' take on mechanics. Since the ...
Not a chance's user avatar
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0 answers
40 views

Topological illustration of spacetime dilation: which function should I use for isometric lines spacing?

Scientific popularization, when it comes to illustrating spacetime dilation around massive objects, often relies on the description of a two-dimensional square-grid, which can be regarded as a cross-...
olivierlambert's user avatar
2 votes
0 answers
51 views

Adding damping to a spring Lagrangian [closed]

I have written a program that produces a Lagrangian. Additionally, I need damping for the spring I am simulating in the Lagrangian. Here is the code: ...
Mo711's user avatar
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1 vote
2 answers
168 views

How to solve Relativistic Lorentz Force equation if $\gamma$ is not constant?

I am trying to numerically obtain the trajectory of an electron inside a periodic magnetic field $\mathbf{B}$, taking into account that the relativistic factor $\gamma$ is not a constant (the electron ...
Joan Arenillas's user avatar
2 votes
0 answers
70 views

Calculating higher-order correlation functions of the Ising model

I'm trying to compute the correlation functions $<s_1...s_n>$ of specific n-spin subsets as a function of the temperature in systems with up to $N=256^2$ spins. These will be used to compute ...
Ibrahim Khalil's user avatar
0 votes
2 answers
83 views

Initial positions and velocities for the three-body problem

I have made a simulation of the three-body problem, it follows the euler's method of solving differential equations. I have tried some initial positions and velocities of the bodies and have observed ...
Ronny's user avatar
  • 166
1 vote
1 answer
70 views

Numerically solving frame-dragging equation in Hartle-Thorne formalism

I'm trying to write a Python code to implement Hartle-Thorne approximation formalism for rotating neutron stars. In this formalism, I am required to solve the following second order differential ...
abirbhav's user avatar
1 vote
2 answers
62 views

Numerical solution of differential equations, e.g. the three-body problem

What forms of differential equations have numerical solutions with errors that go to zero with sufficient computational power? For example, suppose I want to solve a differential equation $E$ for a ...
Alex's user avatar
  • 125
3 votes
1 answer
41 views

Gravitational wave flux in Effective One-Body (EOB) models

I'm working for my M2 internship on gravitational waves in effective one-body approach, and I'm struggling in understanding how they compute the non-conservative flux from GW radiations. Most of the ...
Thomas Gabel's user avatar
-1 votes
1 answer
74 views

Yet another question on time dilation on basic special relativity (with code) [closed]

I've been trying the book Computation Physics and came up with the following exercise: Exercise 2.4: A spaceship travels from Earth in a straight line at relativistic speed v to another planet x ...
Dimitri's user avatar
  • 161
2 votes
0 answers
57 views

Unique numerical solution to Lippmann-Schwinger (Fredholm) equation

I am working in non-relativistic scattering theory and solving the Lippmann-Schwinger equations for the $T$ matrix in momentum space: $$T_{fi}(k_f,k_i) = V_{fi}(k_f,k_i) + \sum_n\int_0^\infty \frac{V_{...
quixedjetr's user avatar
1 vote
0 answers
45 views

Inconsistency in numerical and slow-roll solutions of Mukhanov-Sasaki equation during Inflation

from my lectures in cosmological inflation, we derived the Mukhanov-Sasaki equation and its initial condition (Bunch-Davies). From here, it was of our interest to find a numerical solution of the ...
Jules Alvarez's user avatar
0 votes
1 answer
88 views

Where is the orthogonality center of the AKLT ground state matrix product state?

It is a known fact that the ground state of the 1D Affleck-Kennedy-Lieb-Tasaki model (AKLT) can be represented as a matrix product state (MPS) of the following form: $$ \left|{\psi}\right\rangle = \...
Yoav Zack's user avatar
  • 167
1 vote
2 answers
75 views

Static solution to an implicitly dynamic problem - heat equation

Heat equation This is the heat equation: $ \frac{\partial u}{\partial t} = \frac{\partial^2 u}{\partial x^2} + \frac{\partial^2 u}{\partial y^2} + \frac{\partial^2 u}{\partial z^2} $ ...
Megidd's user avatar
  • 123
0 votes
0 answers
38 views

Force-simulation for graph layout: How to avoid particle collapsing into a single point?

In a force-based graph-layout simulation using Barnes-Hut, what are the conditions for collapse? With collapse I mean multiple (or even all) nodes "collapsing" into a single point. Is there ...
skep's user avatar
  • 1
2 votes
1 answer
63 views

Finite differencing for velocity cross terms?

In writing down the Navier-Stokes equation I have encountered two equations as follows: $$ 4\frac{\partial^2 v_x}{\partial x^2} + \frac{\partial^2 v_x}{\partial y^2} + 3\frac{\partial^2 v_y}{\partial ...
Raj Upadhyay's user avatar
1 vote
1 answer
52 views

Magnetic force expression in COMSOL, what does the T stand for?

During a recent project I've used COMSOL to help evaluate the force excerted on a steel ball from an electromagnet. The formula used by COMSOL is: \begin{equation} \textbf{F} = \int_{\partial\...
NL195's user avatar
  • 11
1 vote
0 answers
22 views

Any quantum Monte-Carlo algorithm for calculating the lowest eigenenergy in each symmetry sector?

Suppose we have a hamiltonian which has the parity symmetry (e.g., the Heisenberg model with the open boundary condition). Is there any quantum Monte-Carlo algorithm which can be used to calculate the ...
poisson's user avatar
  • 1,957
2 votes
0 answers
54 views

Is there a proof for critical slow-down in Monte Carlo?

It is physically understood why the standard Metropolis-Hasting algorithm slows down near the critical temperature, since it doesn’t utilize the divergence of the correlation length. However, I’m ...
Andrew Yuan's user avatar
  • 2,123
1 vote
3 answers
99 views

Volume change of a deformable cylinder with a uniform spinning angular velocity

Consider a deformable cylinder without gravity with a uniform spinning angular velocity and the cylinder is not in contact with anything. In theory this cylinder shouldn't change its cross sectional ...
feynman's user avatar
  • 85
1 vote
1 answer
65 views

Solving partial differential equations using MacCormack scheme and to quantify in what situations this scheme is stable using von Neumann stability

I am trying to simulate Alfven waves and for that, I need to solve partial differential equations using the MacCormack scheme. The predictor steps are: \begin{align} u^p_j&=u_j^n-c\left(b_{j+1}^n-...
subrojitroy's user avatar
0 votes
0 answers
63 views

Hermiticity of Majorana Fermions: SYK Model

The SYK Hamiltonian is defined as $$H = -\frac{1}{4!}\sum_{i,j,k,l=0}^{L-1} J_{ijkl} c^x_{i}c^x_{j}c^x_{k}c^x_{l},$$ where $J_{ijkl}$ is a random all-to-all interaction strength which is normally ...
Young Kindaichi's user avatar
-1 votes
1 answer
102 views

Tychonian Universe [closed]

I am struggling with calculations that are required in a sub-section of a paper that I am writing: The retrograde motion of a Tychonian Universe from a Martian frame of reference. I have found the ...
phy_theo's user avatar
0 votes
1 answer
84 views

Solving divergence and curl equations numerically

I've recently come to learn about Jefimenko's general solution for Maxwell's equations as well as the FDTD method in electromagnetic optics, and that has got me thinking whether I myself can solve ...
Lagrangiano's user avatar
  • 1,616
0 votes
0 answers
36 views

Studying behaviour of a Klein-Gordon field inmersed in a classical electric field

I want to study the behavior of a 1+1 dimensional Klein-Gordon field immersed in a classical constant electric field, in the context of backreaction, i.e. I calculate the solution to the Klein-Gordon ...
dolefeast's user avatar
  • 170
0 votes
0 answers
23 views

Zou He boundary condition for Lattice Boltzmann

I am utilizing this paper "https://arxiv.org/pdf/0811.4593.pdf" to implement the Zou-He boundary condition, aiming to enforce a velocity of 1 at the inlet of the complex geometry. The ...
Resa's user avatar
  • 1
0 votes
1 answer
82 views

Method of characteristics with coupled ODEs

I am having trouble following the derivation in this paper https://arxiv.org/abs/1810.07775 using the method of characteristics. By using the method of characteristics, they derive the following ODEs ...
Idieh's user avatar
  • 71
1 vote
0 answers
31 views

Cluster Monte Carlo algorithms for $n$-body interactions

Suppose I wanted to perform a Monte-Carlo numerical simulation of an Ising-like model, with a Hamiltonian of the form $$ -\beta H = J \sum_{\langle i j \rangle} \sigma_i \sigma_j + g \sum_{ijk\ell \in\...
Zack's user avatar
  • 3,098
2 votes
1 answer
127 views

Ball trajectory in the game of pétanque - unexpected drag results

Context A classmate and I (about college level, not physics majors)need to evaluate the different physical factors at play during a game of pétanque. We thought about estimating the importance of air ...
François Mortier's user avatar
2 votes
0 answers
48 views

DFT total energy from band energy

I'm using Kohn-Sham DFT as a part of my research. The material is metallic crystal. In the following, you can assume that $\rho$ refers to the density matrix and $H$ refers to a hamiltonian matrix ...
Mikke Mus's user avatar
  • 121
1 vote
2 answers
62 views

Numerical resolution of Schrödinger 1D Time Independent Equation, why do Energies not following the expected pattern? [closed]

I want to solve numerically the 1D time independent Schrödinger: $$-\dfrac{\hbar^2}{2m} \dfrac{d^2 \psi(x)}{dx^2} + V(x)\psi(x) = E\psi(x)$$ For starter, lets say we solve the Particle In a Box ...
jlandercy's user avatar
  • 255
0 votes
2 answers
80 views

$N$-body gravitation simulation in 2D and 3D

My question is quite general. I want to make $N$-body simulation, for example galactic dynamics, using $N$ stars. One possibility is to make these calculations in 2D using an inverse square law and ...
Rémy Galli's user avatar
0 votes
0 answers
31 views

Admissible solutions for waves propagating in a fluid medium obtained from Fast Fourier Transform

Given a two-dimensional pressure distribution $p(x,y)$ in a fluid medium, we can perform Fast Fourier transform to obtain the amplitude and phase spectra. The 2D-FFT (and eventually, the IFFT) ...
Alucard Nosferatu's user avatar
2 votes
0 answers
96 views

Numerical Relativity for Computer Scientists

What resources on numerical relativity/simulation would be suitable for a primarily theoretical computer science background [algorithms analysis, complexity theory, etc.]? Importantly, while I'm ...
0 votes
0 answers
50 views

How to properly discretize and solve the Liouville equation?

Consider some dynamical system $\dot{\textbf{X}}(\textbf{x},t)=F(\textbf{X})$ where $\textbf{X}$ is discretized along a 1-dimensional spatial coordinate $\textbf{x}=(x_1,\dots,x_N)^T$. Let $\rho(\...
thespaceman's user avatar

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