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.

learn more… | top users | synonyms

2
votes
1answer
129 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 ...
2
votes
0answers
30 views

How can the fictitious mass in the Car-Parrinello method reproduce the “real” dynamics?

In the Car-Parrinello method, to solve simultaneously the classical equations of motion for the atoms and the Kohn-Sham equations for the electrons, the following effective Lagrangian is used: $$ ...
2
votes
0answers
30 views

Mass scaling in molecular dynamics

I've noticed some authors scale the mass of particles in molecular dynamics simulations while leaving the force field parameters the same in order to achieve materials of different densities. Does ...
2
votes
0answers
114 views

How to compute matsubara frequency summation over computer?

Matsubara frequency sum usually takes the following form: $S_\eta = \frac{1}{\beta}\sum_{i\omega_n} g(i\omega_n).$ But in my problem, $g(i\omega_n)$ is a lengthy expression, which can not be ...
2
votes
0answers
28 views

Coefficients and Parameters for contracted Gaussian basis sets

This is a repost from Chemistry.stackexchange in the hopes that someone here will be able to help me. Any help at all would be greatly appreciated. As far as I understand, an STO-NG contracted ...
2
votes
1answer
141 views

Unexpected eccentricity in moon orbit simulation

I've used Mathematica's NDSolve function to calculate the orbit of the Moon around the Earth. I used the following initial positions (perigee): ...
2
votes
0answers
85 views

Doing numerics in physics [closed]

Soon, I am going to write my master thesis in theoretical physics. I assume there, and later on in my career, I will have to do more serious numerics than I did up to this point. That's why I want to ...
2
votes
0answers
63 views

Euler equation with single state variables [duplicate]

I want to simulate a flow using the Euler equations. For this reason I'm wondering if there's a modified version of the Euler equations. At the moment my formula looks like this: $$ ...
2
votes
1answer
128 views

How much computer power would we need to model every physical aspect of the universe [closed]

So I know there are equations that give you the total energy in the Universe(Friedman). So about if we we to simulate every single interaction from neurons to physical forces, strong and weak, ...
2
votes
0answers
270 views

simple MHD simulation code for (self) education and play with [closed]

I would like some super simple computational code for solving magnetohydrodynamics problems. High accuracy nor performance is not my concern. I wan't it just to visually explore qualitative behavior ...
2
votes
0answers
57 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 ...
2
votes
0answers
170 views

Detailed procedures of numerical calculations in lattice models [closed]

I am looking for a reference to show me a detailed procedure of numerical calculation of a physical quantity of a lattice. I have knowledge of the physics part and I am able to find it. My problem ...
1
vote
1answer
930 views

Why do people use C++ in Computational Physics? [closed]

Once day, I talked to my Prof. about Computational Physics and he showed me his work. I'm quite surprised that why Prof. use C++ for computation because C++ quite complicated. I heard he talked about ...
1
vote
3answers
133 views

Why does the Metropolis algorithm allow changes even for ∆E > 0?

In the Metropolis Monte Carlo algorithm, why can you accept changes even for ∆E > 0 (provided that a random number is less than a given probability ratio, e.g. exp(-β∆E))?
1
vote
2answers
149 views

What is a good model for computing water dropping on a surface?

Before introducing my question I would like to outline the fact that I'm a coder, so I can be wrong when using some kind of terminology. What is a good model for computing the flow, the shape and all ...
1
vote
3answers
864 views

Non-computable numbers in Physics

It is known that there are real numbers that can't be calculated (non-computable numbers). Quite probably that some physical phenomena (it is possible still undetected) depend on this numbers. Whether ...
1
vote
1answer
210 views

I'm getting weird autocorrelations when simulating an Ising model below the critical temperature

So I'm simulating an Ising model using Monte Carlo and the Metropolis algorithm. After letting it reach equilibrium, I try to calculate the autocorrelation of the magnetization. As long as the system ...
1
vote
2answers
1k 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, ...
1
vote
3answers
105 views

Textbook recommendation for computational physics

Can anyone recommend some good textbooks for undergraduate level computational physics course? I am using numerical recipe but find it not a very good textbook.
1
vote
2answers
572 views

Acceptance probability 2D Ising Model

Disclaimer: I just found a possible solution - eventhough i don't really understand, whats wrong with my prior approach. Edit: I just tried to calculate it from scratch and found the following: $E ...
1
vote
2answers
299 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} ...
1
vote
3answers
840 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): ...
1
vote
1answer
66 views

Finding the initial velocity vector of an orbiting body

I'm writing a program that simulates Newton's law of universal gravitation by simply calculating the force and applying it on the objects. The simulation works very well, but now I want to simulate ...
1
vote
1answer
253 views

Turning a finite difference equation into code (2d Schrodinger equation)

I am trying to convert the following finite difference equations into code (taken from the bottom of page 12 of this thesis by Maike Schulte Numerical Solution of the Schrodinger Equation on Unbounded ...
1
vote
1answer
97 views

Is there a normalized form of the Euler equation discretized with finite volumes?

I want to calculate a flux on my fpga using the Euler equations with the finite volume method. Unfortunately the values of the state variables differ a lot. For example the pressure has a value of ...
1
vote
1answer
134 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 ...
1
vote
1answer
178 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 ...
1
vote
1answer
77 views

Kernel normalization in Smoothed Particle Hydrodynamcs

I am trying to write some code for a fluid simulation. I have read about Smoothed Particle Hydrodynamics (SPH) and my question is related to the properties of the smoothing kernel. How do I set the ...
1
vote
2answers
73 views

Difference in calculated and simulated ellipsies

My task here is to determine orbit parameters, using current values: $\mu=GM$ - standard gravitational parameter $r$ - distance to the object with Mass $M$ $v$ - speed of the object in the point $r$ ...
1
vote
1answer
70 views

Getting nonphysical results when solving for the index of refraction of a slab?

I'm trying to computationally find the refractive indices (real and imaginary) for a thin slab suspended in air (so the only indices to deal with are air and my material's). I've experimentally taken ...
1
vote
1answer
151 views

Smoothed Particle Hydrodynamics, Chemical Reactions and Stiffness [closed]

Dear people from stackexchange physics. I have been using SPH for quite a while to simulate free boundary flow, and just recently we tried to include some kind of (simple) chemical reaction in our ...
1
vote
2answers
103 views

Discrete approximation of charge density

Given the electric potential $\Phi(r)$ and the Poisson's equation: $$ \nabla^2 \Phi(r) = - 4\pi \rho(r)$$ Consider the 2-dimensional case and let's say that I want to discretize this using a square ...
1
vote
1answer
132 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 ...
1
vote
1answer
127 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 ...
1
vote
2answers
315 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 ...
1
vote
1answer
391 views

Does the universe follow a general physical and computational principle of evolution?

Evolution is a principle in biology, whereby organisms evolve their ability to replicate and multiply in numbers over successive generations. From a computational point of view, the organisms employ a ...
1
vote
1answer
595 views

Calculating Kramers-Kronig using Mathematica [closed]

First of all, I know there is a Mathematica group in beta, but I don't think the problem of the following is directly a Mathematica issue. I am trying to calculate the change of the refractive index ...
1
vote
1answer
51 views

Anyonic braiding statistics from density matrix renormalization group (DMRG) simulations

How does the ground state energy of the system change when we braid two anyons? Can the braiding of anyons be simulated with a computational method such as the density matrix renormalization group, ...
1
vote
1answer
83 views

How to measure the spin-spin correlation in a Monte Carlo simulation of the Ising model?

I'm simulating the Ising Model in 2D up to 5D and I want to calculate the spin-spin correlation, correlation length, and critical exponent of the system. What is a good way to go about doing this? ...
1
vote
1answer
45 views

Thermal conduction through 1D rod with changing thermal diffusivity?

I've been working with solving partial differential equations in 1D numerically using the finite difference scheme. My case is for example this: I've got a rod that's insulated around the sides such ...
1
vote
1answer
167 views

Why is the ground state energy of the Heisenberg XXZ Model unbounded for some values of $J$?

At the moment, I'm looking at numerically studying the Heisenberg XXZ model. The Hamiltonian is given below: $$ H=\sum_{j=1}^{N-1}\left(J S_j^z ...
1
vote
1answer
127 views

A puzzle of thermalization in simulating the 3D XY-model

I am learning the classical Monte Carlo simulation. When I simulate the 3D XY-model $$ \beta H = -\beta J \sum_{<i,j>} cos(\theta_i-\theta_j) $$ where $\beta$ is the inverse of the temperature ...
1
vote
1answer
121 views

Ground state Phase Diagram of Bose-Hubbard Model

The Hamiltonian of Bose-Hubbard model reads as $$H=-J\sum\limits_{<i,j>}b_i^{\dagger}b_j+h.c.+\frac{U}{2}\sum\limits_{i}n_i(n_i-1)-\mu\sum\limits_in_i~~~~~~~~~(1)$$ For this we plot phase ...
1
vote
1answer
60 views

Calculate Euler equations of fluid dynamics without division?

I'm working on the calculation of the Euler equations with the finite volume method. Unfortunately I'm not allowed to do a division. So I'm wondering if there's a form which does not need a division. ...
1
vote
1answer
112 views

Rigid body collision, 3 circles in contact

I'm working on a 2d physics simulation. It's a continuous time simulation, that is, it uses swept shapes over the time-frame and geometrical/vector 'analysis' to determine most immediate time of ...
1
vote
1answer
92 views

Motion of rigid body system in absense of work

In the absence of work on the system, is there a closed form equation for the motion of a set of constrained rigid bodies (let's say, using Revolute (ie: simple pivot) constraints)? If the bodies are ...
1
vote
1answer
75 views

what is two species Bose Hubbard Model? what chage it takes on Fock basis representation?

The Hamiltonian will look like \begin{equation} \ H= -t^a\sum_{<i,j>}^{}(a_i^\dagger a_i + h.c.)-t^b\sum_{<i,j>}^{}(b_i^\dagger b_i + ...
1
vote
1answer
516 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 ...
1
vote
1answer
125 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 ...
1
vote
1answer
309 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. ...