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.

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2answers
964 views

Calculating internal energy of formation

I'm working on some code to simulate combustion at constant volume instead of constant pressure and I need to calculate the internal energy of formation for the species involved because I can only ...
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1answer
34 views

Computing Bottlenecks

On a desktop computer, what are common bottlenecks (RAM vs. CPU, single vs. multithread) on numerical calculations? I'm specifically most interested in exact diagonalization and other methods (EDIT: ...
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27 views

Computation. Problem with numerically solution system of PDE in Mechanics [closed]

Good evening, I have a big problem with num.solution NDSolve of differential equation. To start with, the model: There is a fast-moving rope in closed path. Where $T$ is tension, $a$ is angle beetwen ...
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2answers
44 views

Using computational physics to calculate acceleration in a pulley system [closed]

I am trying to calculate the acceleration of this simple pulley system: Up until now I was able to take into consideration the two weights, the mass of the pulley and the friction between the pulley ...
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2answers
148 views

What is meant exactly by “renormalization” in condensed matter physics, specifically in density matrix renormalization group (DMRG)?

I first encountered the concept of renormalization in the context of statistical physics. Here, the renormalization "group" is a set of transformations of the system such that the Hamiltonian $H(J,\...
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1answer
1k views

What is a stoquastic Hamiltonian?

Recently, I've often read about the term 'stoquastic Hamiltonian'. But I couldn't find a precise definition anywhere. I found that the Ising-Hamiltonian is a stoquastic Hamiltonian, but that does not ...
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1answer
112 views

FEM: Distributed loads over adjacent quadratic bar elements

I am an electrical engineering student trying to teach myself Finite Element Methods (FEM) through a couple of textbooks and independent study. While I believe that I understand the basic ideas ...
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26 views

Lens phase mask on a laser beam profile in Fourier space

I have a Gaussian laser profile on which I want to apply a phase mask that acts like a lens. The phase mask is given by $$M_{lens} = \exp\left(-i\frac{k}{2f}(x^2 + y^2)\right)$$ where $x$ and $y$ are ...
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28 views

Is there any library or mathematica package to computing things like collision term or find distribution function of Boltzmann equation?

Today there is a lot of package in mathematica or another library that are very useful, like SARAH for particle physics. But actually I am working with particle physics in early universe. In another ...
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1answer
28 views

Modelling a particle under the influence of an electric field with a restoring force

Suppose I have a particle under the influence of an electric field. The particle is also attached to a spring. The particle should therefore feel the influence of two forces such that the total force ...
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2answers
67 views

Lift of an airfoil: viscous vs inviscid results

I am trying to understand the difference between the lift computed with an inviscid solver (Euler equations) and the one computed with a viscous solver(Navier Stokes equations). At this point, I ...
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1answer
37 views

Bypass valve, pressure and flow rate

I have no background in thermodynamics or fluid dynamics, so please bear with me. Refer to the following figure: A working fluid with a flow rate of $1~kg/s$ enters a heater at a pressure of $1~MPa$ ...
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40 views

How to draw quiver plot for complex-valued electric field?

I have a matrix of complex numbers for the electric field inside a medium. Since I want to draw the quiver plot of these elements, it will be completely different if I only use the absolute part. Then ...
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31 views

Tight Binding Hamiltonian simulation help

Just want to make sure I am setting this up correct. I am trying to find the eigen energies for a tight binding Hamiltonian, let's say with nearest neighbor hopping term $t$. We can solve for the ...
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27 views

Does the mass of a rigid-body affect its bounce?

I'm working on a computer program which involves some physics. I want to know if the mass of a perfectly rigid ball will affect how high it bounces off the ground. I'm in high school and I haven't ...
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0answers
52 views

Using MATLAB to simulate the Ising Model [closed]

I am using MATLAB to simulate a 1D Ising Chain. I am running into an issue where when trying to find heat capacity, my system has a tremendous amount of noise. I'll post my code and an image of the ...
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2answers
974 views

Interpretation of Stiffness Matrix and Mass Matrix in Finite Element Method

I would like to have a general interpretation of the coefficients of the stiffness matrix that appears in FEM. For instance if we are solving a linear elasticity problem and we modelize the relation ...
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0answers
11 views

flow distribution in pipes incl. hydrostatic pressure

Imagine a system like this: A pipe fed from a pump branch into different branches, it's not a closed loop. There are non-negligible differences in elevation between the pipes. My goal is to ...
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0answers
25 views

Help with diagonalizing a BdG Hamiltonian

I am working on a simulation which diagonalizes a BdG Hamiltonian; let's start with one of the form: $$\hat{H}=-t\sum_{<r,r'>,\sigma}\hat{c}^\dagger_{r\sigma}\hat{c}_{r'\sigma}+\sum_{r}\Big(\...
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1answer
41 views

Useful resources and softwares for computational astrophysics

I am recently working on computational astrophysics. My research is mainly focused on accretion processes around compact objects (black holes & neutron stars), radiative transfer and modelling of ...
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1answer
122 views

Heat transfer in solidification of cylindrical billet

I am trying to plot IN MATLAB the temperature profile of solidification of metal in manufacture of cylindrical billets. The metal is solidifying and the billet moves downwards as a constant water ...
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1answer
1k views

Intuition for when the replica trick should work and why it works

I am a graduate student in mathematics working in probability (without a very good background in physics honestly) and I've started to see arguments based on computations derived from the replica ...
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18 views

Which method can solve the largest number of TISEs?

In my physics studies, we often used separation of variables (or other strong assumptions) to make the problem of solving the 3D TISE more manageable to solve numerically or analytically. In contrast,...
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Spectral Numerical solution using Fourier Transform (FFT) and Chebyshev

How can I solve this equation using FFT in x and z direction and Chebyshev in the y-direction. $ (L_{mn} + \partial_t M_{mn})\hat{q}_{mn} = A_{mn} \sum\limits_{k + p = m} \sum\limits_{l + q = n} [D^...
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1answer
59 views

How do you find the initial velocity and angle required to hit a coordinate and a certain height?

Problem For a game engine I'm writing, I need a function that returns the initial velocity and angle of a projectile launch, such that the affected object reaches a given maximum height, and ends up ...
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1answer
45 views

Computational Physics Books [duplicate]

I'm really interested on how to simulate physical systems that I'm currently studying as a first year student at University. For example, how to replicate a Pendulum using different algorithms (Euler'...
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2answers
55 views

What is the easiest way to do basic mechanical simulations? [closed]

I am interested in doing basic mechanical simulations, such as experimenting with the brachistochrone problem (path of quickest descent) and the motion of point particles under the influence of ...
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0answers
29 views

Matrix Used for Orbital Motion [duplicate]

this question is by no means a new question, however previous questions have been unable to exactly answer my question. I'm attempting to obtain analytical results and then plot the results of a ...
3
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1answer
990 views

Determing Velocity of Moons

I have a question that I believe is relatively easy to answer, I am working on an $N$-body simulation of a fictional star system and am having trouble finding the velocity of moons so that they will ...
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0answers
54 views

Magnetization in a finite lattice Ising model generated with MC algorithm

I generated an Ising model using a Monte-Carlo algorithm and then computed the absolute magnetization per unit volume: $|M|$ and magnetic susceptibility $\chi$ as a function of the temperature $T$ at ...
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1answer
113 views

Master equation for the mechanical modes

Consider the standard model of optomechanical systems with a single optical cavity mode coupled to a mechanical oscillator, which is canonically modeled as a FP cavity with one fixed mirror and one ...
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0answers
19 views

What is computable and independent of subtraction scheme?

I am trying to compute, using mathematica, the renormalization $Z$s (of the field, mass and coupling) in $\phi^4$ theory (using dimentional regularization). I have done so in two different ...
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2answers
60 views

Question about FFT analysis of a signal

In labs we had to measure the oscillations of a pendulum using an electric sensor. So basically, my data consists of time and voltage (which represents amplitude) pairs. The task was then to perform ...
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1answer
92 views

DFT: When would one use a LDA over a GGA method?

Computationally using Density Functional Theory (DFT), is there any examples where Local Density Approximation (LDA) would be preferred over using Gradient Generalized Approximation (GGA) methods for ...
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33 views

Ground state of nonlinear schrodinger equation

can any one help me to found the ground state of nonlinear schrodinger equation like the result of Edwards and Burnett, 1995, using mathematica or matlab.
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58 views

Implications of thermodynamic inconsistency in CFD calculations

During my PhD work I had to use tabulated values of thermodynamic properties of gases in some Computational Fluid Dynamics (CFD in short) simulations. CFD simulations consist in the numerical solution ...
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1answer
335 views

Issue with Bifurcation Plot for Driven Pendulum

I'm trying to create a bifurcation plot for a driven damped pendulum. In particular, I'm trying to recreate the plot found in Taylor's 'Classical Mechanics' (page 484) for a driving strength $\gamma$ ...
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2answers
147 views

Hydrogen in a box

I would like to approximate the 1S wave function of a system constrained to a box $\{(x,y,z)|x\in[0,a],y\in[0,b],z\in[0,c]\}$, subject to the potential of the hydrogen atom. I have proposed the ...
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1answer
198 views

Maxwell's equations UPML in FDTD with inhomogeneous media

I'm looking at matching the UPML (uniaxial perfectly matched layer) defined in Taflove&Hagness' Computational electrodynamics to an inhomogeneous media (inhomogeneous w.r.t. both $\varepsilon$ and ...
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1answer
78 views

How to test the physical accuracy of a finite difference solution to Laplace equation?

I just wrote a program that computes the potential field inside a Penning-Malmberg trap; my end goal is to simulate plasma inside this trap. First I need to make sure my potential field across the ...
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0answers
43 views

Good introductory book to computational physics [duplicate]

First time asking a question here. As per the title I'm trying to find a decent book that serves as an introduction to computational methods used in physics. A little background on myself will help ...
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1answer
172 views

How to calculate the min Energy in SCF Hartree Fock Calculation?

I have just started writing a program using Hartree-Fock approximation. I have constructed my Hamiltonian (4 by 4 matrix, number of states=4) and found eigenvalues and eigenvectors(4 eigenvectors with ...
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0answers
43 views

Magnetic susceptibility

Currently I'm doing the simulation of Ising Model with Monte Carlo method. I got a curve which the magnetic susceptibility diverge (precisely due to finite size effect, it is not diverge but show the ...
3
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1answer
89 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 ...
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1answer
168 views

Solving the Schrödinger equation numerically on a non-uniform grid

I am currently developing a numerical solver, which solves the standard, one-dimensional, time-independent Schrödinger equation $$\frac{-\hbar^2}{2m}\frac{d^2\psi}{dx^2} + V(x)\psi = E\psi \tag{1}$$ ...
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1answer
99 views

Why are numerical solutions for the Schrödinger equation necessary to plot this free waves solution?

Suppose a particle in free space given by: $$\psi(x,t) = Ae^{ik(x-\frac{\hbar k}{2m}t)} + Be^{-ik(x-\frac{\hbar k}{2m}t)}.$$ Why are numerical solutions necessary in order to plot this? Why can't ...
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1answer
134 views

Numerical solutions for time-dependent Hamiltonian

Currently I am facing the problem to solve numerically the following equation for a double well harmonic potential: $$i\hbar \frac{\partial}{\partial t}\psi(x,t)= -\frac{\hbar}{2m}\frac{\partial^2}{\...
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29 views

Can we invert Density Functional Theory through sufficiently accurate experiment?

The famous Hohenberg-Kohn theorems say that there is a one-to-one mapping between the many-body Hamiltonian, $\mathcal{H}$, of a solid and its ground-state electron density $\rho(\mathbf{r})$. As far ...
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1answer
115 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 ...
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3answers
146 views

Numerical method for first-order non-linear differential equation

So I'm modeling a cycler on a 1000 m race track using the equation $$\frac{dv}{dt}=\frac{P}{m}\left(\frac{1}{v}\right)-\frac{k}{m}\left(v^2\right)-ug$$ where $P$ = power, $m$ = mass, $v$ = velocity of ...