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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1answer
27 views

What's wrong with my DFT implementation?

I am trying to write an implementation of the discrete Fourier transform myself in Python, but for some reason, the transform that I get out is wrong. There are no fancy tricks in my implementation, I ...
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1answer
121 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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Slow converging in Monte Carlo due to Shell effect

While I was reading materials, the author mentioned that Monte Carlo converges slowly due to shell effect while filling the single particle states, but using a twisted boundary will make it go much ...
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1answer
36 views

How to calculate acceleration due to gravity in a 3D $N$-Body system?

How do you calculate acceleration due to gravity for objects in 3D space? My current understanding for the force due to gravity on object $i$ from object $j$ is $$\mathbf{F}_g=(\mathbf{r}_j-\mathbf{r}...
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Modeling of Spatial Filtering of aberrated beam (~10mm) with Pinhole (~10μm) in 4f-Configuration -> size-constraints

I am trying to simulate a spatial filter in 4f-Configuration with an aberrated input beam to get a feeling for the remaining intensity and wavefront error depending on the pinhole size & ...
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2answers
55 views

Using Runge-Kutta method with measurements of acceleration (what to do with half-steps?)

I'd like to perform a short-time motion estimation based on measurements from an Inertial Measurement Unit. If I use the Runge-Kutta method, I will need to compute the k values at half-time steps (Ref)...
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1answer
27 views

Height oscillations in orbit induced from lunar gravity

I am trying to numerically solve the orbit of a space probe around the moon in a non-spherical gravitational field . $ \Large \begin{align} \frac{d^{2} x}{dt^2} = - \frac{G M x}{(x^2 + y^2)^{3/2}} - \...
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40 views

Energy conservation in numerical orbital motion [closed]

I am trying to numerically solve the orbit of a space probe around the moon in a non-spherical gravitational field . FOR AN UPDATED VERSION GO TO: Height oscillations in orbit induced from lunar ...
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1answer
52 views

Modelling sky noise using a 2D array with plane waves

I have a question about modeling sky noise which should be filtered by a spatial filter 4f system. My approach for this task is to use a 2D array with random amplitude values and another 2D array that ...
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1answer
25 views

Apparent horizon buildup in a BH merger

I just read some articles about binary BH merger simulation. These state that at a certain instant a common apparent horizon(or MOTS) appears, surrounding the two BHs. This instant is called the ...
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Which is the Best Free Physics Simulator that can simulate the dropping of a ball? [duplicate]

We were asked in class to use a physics simulator beforehand to test the conditions of an experiment we are going to do and save it to use in our report. The experiment involves the dropping of a ball ...
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How to note Right Ascension and Declination equatorial coordinates in decimal? [closed]

For me is common to see RA noted as 16h 55m 43.385s and DEC as -41° 38' 36.472". I'm trying to develop a program that will ...
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1answer
38 views

Reducing the Hamiltonian size by using a symmetry to speed computations

Say I have some Hamiltonian $\mathcal{H}$ that describes a 1-D spin chain (i.e. Heisenberg model) which has a number of compatible symmetries $\{\mathcal{O}^i\}$ (i.e. total spin...etc). For all $\...
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1answer
311 views

Why does my Hartree Fock/SCF code work for small molecules (water, methane etc) but goes crazy for slightly larger ones (Benzene, Butadiene etc)?

I made a Hartree Fock code, in the psi4 package, following the formulas given on this page: http://sirius.chem.vt.edu/wiki/doku.php?id=crawdad:programming:project3 When I use the same geometry they ...
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1answer
28 views

Numerical modeling of induced voltage

I have an arbitrary magnetic field that varies with time, and I'm trying to numerically model the induced current in a resistive loop over time. Details below. I'm building an electromagnetic ...
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2answers
327 views

General Relativity and Computing with Tensors

In Riemannian Geometry (or Pseudo-Riemannian too), all of the operations performed are in general position dependent. For example, the metric tensor $g_{\mu\nu}(x)$ is dependent on position $x^i$ for ...
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2answers
388 views

Obtaining Transmission Coefficient of Beam Upon a Linear Potential

I would like to determine the transmission coefficient $\mathcal{T}$ for a particle beam $$\Psi(x,t) = A_o e^{ikx}e^\frac{-iE_ot}{\hbar}$$ with energy $$E = \frac{\hbar^2k^2}{2m}$$ incident upon a ...
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1answer
543 views

Problems while numerically computing band structure using k.p theory

I want to use k.p theory to numerically compute the band structure of a bulk semiconductor. The band I like to include are the lowest conduction band (cb), the heavy-hole (hh), the light-hole (lh) and ...
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1answer
264 views

Which are the best books I can refer for turbulent heat transfer and its computation?

I am a graduate student. I wanted to do computation on heat transfer problem mainly heat convection. I am working on turbulent regime. Can you kindly suggest some good books so that I can get ...
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15 views

For a Thermo-Calc database, is it possible to view the equation/parameters of the Gibbs free energy models?

I want to get the equations that model free energy for a given phase in a given alloy system (see attached image). I do not just want to get values of free energy for specific compositions. Is it ...
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35 views

Using air resistance (drag) in Python calculation

I am simulating a free fall with a function that needs to calculate the time it takes for a particular object to reach the surface, I got this program working without accounting for air resistance.. ...
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1answer
214 views

dVolume/dt= inflow-outflow and ∇⋅𝑣=0

First, I had to say I am very confused about fluid mechanics. Here is one question about continuity question. For the incompressible flow, and density is constant, we have the continuity equation ∇⋅ �...
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20 views

What is the ideal software to simulate a falling maple seed (samara)?

I am completely new to the domain of CFD, so kindly pardon my ill-terminology ;p The task I have requires me to simulate the falling of a maple seed (or an equivalent CAD model) to record its vertical ...
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19 views

4-fermion interaction - vertices calculation with Feynrules

Dear Feynrules users and all physics enthusiasts, I was going to derive the 4-fermion vertices in Feynrules and to pass the generated model further to MadGraph and/or CalcHep. According to the most ...
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25 views

Verifiation the proof of mechanism represent by formula $pv^{(2-\gamma)}$=constant

I was evaluating equation $\frac{du}{dv}=-p$ and $u=\frac{1}{\gamma-1}pv$ which is internal energy of gas,by solving this equation, one will get $\frac{dp}{dv}=-\gamma \frac{p}{v}$,solving this DE ...
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2answers
285 views

Vortex in a Pipe / Solutions or approximations?

I want to study a vortex flow in a pipe; in other words helical flow. A couple introductory texts on fluid mechanics (e.g. Shames, Mechanics of Fluids) describe the solution to vortex flow in 2D: $...
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0answers
28 views

Numerical integration of overdamped Langevin equation: explicit methods?

Assume we have a generic overdamped Langevin equation $$ \frac{d {\bf{x}} }{dt} = {\bf{f}}({\bf{x}}) + B {\bf{w}}(t) $$ where $\bf{f}$ is a deterministic external (and fixed) force field (non ...
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1answer
23 views

How to compute the divergence of a measured vector field?

The divergence a 2D vector Field $\mathbf{F}(x,y) = F_x(x,y)\, \hat{i} + F_y(x,y)\, \hat{j}$ is defined as $$\mathrm{div}\,\mathbf{F} = \bigg( \dfrac{\partial F_x}{\partial x} + \dfrac{\partial F_y}{\...
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3answers
248 views

Numerical complexity of different quantum chemistry approaches

For the introductory course for the students I am trying to collect the brief overview of different quantum chemistry methods and their numerical complexity. The second point is surprisingly poorly ...
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2answers
231 views

Cellular automata and time T

Reading around about various CA models I saw that there are even those who are following the track to provide a single mechanicist model of the universe. For example Gerard van 't Hooft claims that ...
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1answer
51 views

How to choose Pseudopotential for DFT calculation?

I am beginner and newly started running DFT calculations to find out electronic band structure of certain materials in Quantum Espresso.But we have to select the pseudopotential for running scf loop. ...
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1answer
30 views

What is the relationship between lattice field theory and grid-based numerical methods?

I recently learned of lattice field theory wherein quantum fields are defined on a discrete spacetime. Naively this sounds to me a lot like certain numerical methods for solving differential equations ...
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2answers
311 views

Hamiltonian with ext. vector potential - complex kinetic energy

in a given (TD)DFT code with an atomic basis set, i.e. $$ \psi(\mathbf{r},t) = \sum_i c_i(t) \phi_i(\mathbf{r}) $$ (where the non-on-site basis functions $\phi_i$ aren't necessarily orthogonal), the ...
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1answer
264 views

Finite Difference Method Heat Equation problems at boundary between two materials

For a project I am assigned to solve the heat equation in a 2D environment in Python. To do this, I am using the Crank-Nicolson ADI scheme and so far things have been going smooth. I would also like ...
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0answers
32 views

Bond Orientational Correlation Function

Firs this question has some similarity with Bond order correlation function and Bond Orientational Correlation Function - how exactly to calculate but its a little bit different , so having those ...
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1answer
344 views

Convert units of Empirical Orthogonal Function (EOF) for sea surface temperature data

I have a dataset of daily averaged sea surface temperatures for an entire year. I wish to use an empirical orthogonal function to find the dominant patterns within the data. Consider that my ...
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1answer
49 views

Generating Ising model steady state configurations

What is the most efficient way to simulate steady state configurations of the Ising model? I am just interested in having a large set of random steady state configurations of the 1D Ising model (with ...
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1answer
38 views

Restrictions on Initial Values for the first derivatives of a wavefunction, for a bound state in the time independent Schrödinger Equation?

The time independent wave function for a bound state given some potential function $V(r)$ is given by the time independent Schrödinger Equation $$E\Psi=-\frac{\hbar^2}{2m}\left(\frac{\partial^2\Psi}{\...
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1answer
40 views

Do neutron star merger studies probe beyond vacuum GR?

When mergers involving neutron stars and / or black holes are simulated (e.g. when predicting gravitational wave signatures for these mergers), obviously complicated numerical relativity calculations ...
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0answers
16 views

Church–Turing–Deutsch principle

In what sense from the  Church–Turing–Deutsch follows that it is possible to simulate with one physical system all the other physical systems? I know that we can build logic circuits with a Toffoli ...
3
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2answers
116 views

Estimating partition function using Montecarlo methods

While working on a completely unrelated quantum computing problem, I ran into a quantity that can be mapped to a partition function of spins on a triangular lattice. It is not quite an Ising model, ...
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2answers
60 views

How can I quantify the “temperature” of a system that is still evolving?

My system is a bunch of charged particles in a 1 dimensional harmonic potential. This is a computer simulation, and what I get is a list of the positions and velocities of each particle at every time ...
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33 views

Books and courses on Computational quantum mechanics

Can you please suggest the best book and course available on computational quantum mechanics using Mathematica and python or Matlab.
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1answer
43 views

Acceleration function of position and time

I have an acceleration function in python with position and time parameters and returns the acceleration value. I need the end velocity at a position ,start velocity is zero. how to calculate this ...
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1answer
450 views

How do I use Kepler's Laws to propagate an orbit for a Two-Line Element (TLE) Set?

I need to propagate a large number of orbits (get a satellite's position at a certain time) from TLEs (two-line element sets) using Kepler's laws. Ordinarily I'd use a real propagator like SGP4/SDP4, ...
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0answers
15 views

Lattice Boltzmann method: properties of D2Q37 stencil and beyond

I am new in the world of Lattice Boltzmann method (LBM). I have just found in this paper [1] the following statement: A D2Q37 Lattice Boltzmann scheme correctly reproduces the equation of state of ...
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0answers
11 views

Initial Conditions for no-slip velocity (Walls)

For CFD initial condition, I want to know if i have to apply a very high velocity gradient on the wall of a pipe (internal flow) as it's the case when you study the freestream flow which surrounds an ...
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1answer
346 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 ...
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1answer
9k views

Calculating displacement amplitude of ultrasonic power transducer

I am not a physicist, but my current project drives me to some physics-related computations, hence seeking help. I have some ultrasonic transducers, 5938D-25LBPZT, for which very limited information ...

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