# 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.

1,052 questions
Filter by
Sorted by
Tagged with
1k views

### Connection between bond-dimension of a matrix product state and entanglement

The bond dimension is the dimension of the truncated matrix product state (MPS). Let us assume that I am simulating some many-body system with high entanglement via the density matrix renormalization ...
171 views

### Minimal Extension of Wave Equation to Include Dispersion

Let's say you are modeling some process with the wave equation $\frac{1}{c^{2}}\frac{\partial^{2}\psi}{\partial t^{2}} = \nabla^{2}\psi$. You wish to improve your model by including dispersive effects,...
466 views

### How to simulate a crashing wave? [closed]

I'd like to create a very rough animation of a wave crashing on a beach. I'm guessing it would have to be a particle simulator, where you code in the forces between the particles and then integrate ...
979 views

### Why does thermodynamic integration work?

Brief introduction: Thermodynamic integration is a neat computational method used mainly for computing free energy differences between target and reference states of classical many-body systems, such ...
426 views

### Eigenvalue problem for differential equations in QM

I have a very simple question with regard to numerical methods in physics. I want to solve the eigenvalue problem for a particle moving in an arbitrary potential. Let's take 1D to be concrete. I.e. I ...
3k views

### What are the limitations of Smoothed-Particle Hydrodynamics?

I've been excited by some of the possibilities of Smoothed-Particle Hydrodynamics (SPH). I have seen some very exciting demonstrations of their use in 3D graphics, but I am wondering how well the ...
175 views

### Determining bound state masses from a lattice $\phi^4$ simulation

I've recently written a program in python that simulates the $\phi$ to the fourth scalar quantum field theory in a 4 dimensional euclidean spacetime. The lagrangian for this theory is that of a free ...
413 views

### Feynman's infinite amount of logic for one tiny bit of space

Watching one of Feynman's lectures, I came across something that puzzled me. What was Feynman referring to when he said the following? What goes on in no matter how tiny a region of space and no ...
692 views

### Can the Metropolis-Hastings algorithm be generalized to quantum systems?

The Metropolis-Hastings algorithm is an efficient way of simulating classical ensembles using the Monte Carlo method. Is there a generalization of this algorithm to quantum systems? What I DON'T have ...
166 views

### Visualising General Relativity [closed]

I've recently found myself with copies of both Maple and Mathematica and I'm looking to use it to study relativity and hopefully the field equations of GR. I mainly study general relativity but I've ...
314 views

### Computational scaling of quantum and classical Monte Carlo algorithms

How does the computational complexity of finding an equilibrium thermal state for a given Hamiltonian at a given temperature scale with system size under classical and quantum Monte Carlo? I know ...
2k views

### Why do objects in a gravity simulation experience sudden large accelerations?

I'm trying to create a simple program that simulates gravity. The idea is that I have one central sun and several planets that I can create with a swipe gesture on the screen, and I use the initial ...
509 views

### What states are satisfying an entropic area law and why do they satisfy it? More specificly why do matrix product states satisfy it?

I am currently reading some papers concerning the question why the density matrix renormalization group (DMRG) method is working well for simulating one dimensional systems and bad for higher ...
3k views

### What is the next step beyond quantum computation?

Assuming we develop quantum computers one day, what would be theoretically the next step? Would it be string-theory based computers? How would these computers differ performance-wise (ie what can they ...
4k views

### Tight binding model in a magnetic field

The standard way to treat a tight binding method in a magnetic is to replace the hopping matrix element: $t_{i,j}\rightarrow e^{i\int_i^j\mathbf{A(x)}.d\mathbf{x}}$ the so called "Peierls ...
709 views

### Ising model observables

Is there a formula or equation relating $\langle E\rangle$ and $\langle M\rangle$ (average spin per site) and $\langle E^2\rangle$ to temperature $T$ for the square lattice Ising model at zero ...
1k views

### Difference between Monte Carlo and Quantum Monte Carlo methods?

What are the differences between Classical Monte Carlo methods and Quantum Monte Carlo methods in condensed matter physics? If one want to study strongly correlated systems with Quantum Monte Carlo ...
90k views

### How does force affect velocity?

I know that a force will change the magnitude of velocity if it is at an angle other that 90 degrees. If the force is perpendicular to the velocity it will cause the path of the object to curve and ...
604 views

### How is time evolution done in numerical GR?

Suppose we're simulating what happens when a fairly massive object falls into a black hole. Say the object starts far away, so that the initial condition is that the metric is the Schwarzschild metric ...
2k views

### Numerical analytic continuation for Green's function

Recently, I happened to hear about the possibility of doing analytic continuation numerically. That sounds attractive for the ubiquitous $\mathrm{i}\omega_n\rightarrow\omega+\mathrm{i}0^+$ procedure, ...
1k views

### Numerical schemes, time integration algorithms and energy conservation

What does it mean when someone says a numerical scheme or a time integration algorithm is "energy conserving". How can a numerical scheme "gain" or "lose" or "conserve" energy apart from the numerical ...
10k views

### Solving one dimensional Schrodinger equation with finite difference method

Consider the one-dimensional Schrodinger equation $$-\frac{1}{2}D^2 \psi(x)+V(x)\psi(x)=E\psi(x)$$ where $D^2=\dfrac{d^2}{dx^2},V(x)=-\dfrac{1}{|x|}$. I want to calculate the ground state energy(...
2k views

### Physics of simple collisions

I'm building a physics simulator for a graphics course, and so far I have it implementing gravitational and Coulomb forces. I want to add collisions next, but I'm not exactly sure how to go about ...
1k views

### Dirac equation on general geometries?

I have a numerical method for computing solutions to the Dirac equation for a spin 1/2 particle constrained to an arbitrary surface and am interested in finding applications where the configuration ...
310 views

### What advantages have a symplectic or geometric integrator over a simple one, say, RK4?

I heard that a symplectic integration algorithm has a property related to the phase space of a system, but i don't understand much further than that. I'm interested in applying that method to a non-...
1k views

### How to include random force in the simulation (Classical Molecular Dynamics)

I need to implement a random force in my code according to the fluctuation dissipation theorem. I have a Gaussian distribution function ready width average 0 and distribution 1 and I know I need to ...
88 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 ...
2k views

### Difference between real time and imaginary time propagation?

Suppose I want to solve a non-linear Schrödinger equation using imaginary time propagation to get the ground state solution. I choose $t = - i \tau$, and then solve the equation using the split-step ...
121 views

### What's the loss of information in taking the moments of the Vlasov equation for the Particle-In-Cell method

I know that when deriving the hydrodynamic equations from Boltzmann's equation we take the first three moments along momentum space to get the conservations laws. Taking infinitely many moments would ...
3k views

### Should acceleration be included in state vector of a Kalman filter?

I'm developing (actually adopting existing solution) a Kalman filter to model motion of a vehicle (UAV or automobile). The state vector will include position, velocity, and, possibly, acceleration. ...
291 views

### Symplectic integration methods - non-conservative forces

With symplectic integrators, the aim of the game (among other things) is to try and preserve structure of the Hamiltonian - for e.g. conserved quantities like angular momentum. With specific focus on ...
265 views

502 views

### In condensed matter simulations, how is particle number density computed in practice?

I have been reading a recent paper. In it, the authors performed molecular dynamics (MD) simulations of parallel-plate supercapacitors, in which liquid resides between the parallel-plate electrodes. ...
1k views

### Implementing simple atom model using density functional theory (DFT)

I am trying to write computer code which will find the energy and density function for an atom with $Z$ protons and $N$ electrons. I am working in 1D for simplicity and would like to make the overall ...
265 views

### How close to the critical point is sufficient close for measuring critical exponents?

I am learning Monte Carlo and just manage to simulate a phase transition by computing the heat capacity or the susceptibility. I wish I can also compute critical exponents.To this purpose, I have read ...
365 views

### What equation describes the electrostatic potential in these circumstances?

I have a solver for Poisson's equation and it works nicely. It uses finite differences. It works in the presence of multiple dielectrics. It also solves the Poisson Boltzmann equation. That is, fixed ...
940 views

### Numeric method to calculate the charge distribution on a conducting surface?

If I have an arbitrary (closed?) conducting surface and a nearby charge density, is there a simple numeric way of computing the induced charge distribution on the surface?
599 views

### FCC-to-BCC phase transition in NaCl, Buckingham or Lennard-Jones potentials?

Background The transformation from B1 (face centered cubic (FCC) type) to B2 (body centered cubic (body centered cubic (BCC) type) structures is one of the best documented high pressure phase ...