Questions tagged [molecular-dynamics]
Molecular dynamics (MD) is an approach used for simulating dynamic processes through successive integration of Newton's equations of motion.
1
vote
1answer
60 views
Why is detailed balance required for thermodynamic consistency?
why does the Wegscheider condition or detailed balance have to be true for chemical reactions and what does it mean to violate it in terms of thermodynamics?
here is an attempt to derive a simple ...
1
vote
0answers
18 views
Is quantum energy uncertainty underestimated in liquid molecules?
Liquids have the molecular property that the collision frequency (collisions per time) among the molecules is extremely high; it is at the order of picoseconds. Consequently, the Quantum uncertainty ...
0
votes
2answers
25 views
What is the difference between the differents lennard-jones parameters
I know different lennard jones potentials 12-6, 9-6, 9-3. I think the difference between them is the way they describe long-range interactions,but when I use each of them?
Thank you in advance
0
votes
0answers
21 views
How to implement SHAKE algorithm in molecular dynamics for simple systems like linear chain molecule?
3 spherical beads are connected by stiff bond and forms a rod like shape. I am able to perform the Molecular dynamics of them with taking a spring force and a bending force in between them. But for a ...
0
votes
1answer
42 views
Molecular orbital normalization
Suppose that a molecular orbital has the format (not normalized) 0.145A+ 0.844B (1). How do I find a linear combination between A...
0
votes
1answer
26 views
Molecular dynamics: metal clusters
I'm working in molecular dynamics with transition metal clusters. The aim is find the melting point, so, it's necessary scale the velocities to increment temperature.
I know that I should use ...
1
vote
1answer
45 views
When a diatomic ion dissociates, how does the electron density on each atom change?
Let's say, we have a fluorine molecule (F2), and we take 3 electrons from it, so now its bond starts to stretch, and at last the bond breaks and the two atoms are farther and farther away from one ...
1
vote
1answer
35 views
Nose-Hoover thermostat: real-time average problem?
Many articles as well as the following presentation
MD Ensembles and Thermostats, page 23,
claim that the principle of the nose-hoover thermostat is "removing the real-time average"-problem.
I can ...
0
votes
1answer
55 views
Classical Molecular Dynamics Simulations: Who cares about partition functions?
In most introductory textbooks on molecular dynamics simulations the authors usually tell us how the connection between micro and macro is established using the partition function. Knowing the ...
0
votes
0answers
21 views
Why does a phosphor consist of a tiny amount of 'activator' inside a large host crystal?
Why can't you just smear activator (copper, silver, Europium, etc.) on a surface? Why a large 'host' crystal of (usually) zinc sulfide?
0
votes
0answers
17 views
How to perform the rigid body dynamics using velocity verlet in molecular dynamics?
If instead of a sphere we have few rigid cylindrical rods in a box interacting each other by Lennard Jones potential, which obviously will have the tendency to rotate once hit by other rods. For the ...
0
votes
1answer
32 views
Simulate cluster in a heat bath
I want to simulate a cluster in a heat bath. I always thought I had to simulate it first in the microcanonical ensemble (N,V,E) until I reach the equilibrium. In the equilibrium the temperature will ...
0
votes
1answer
25 views
How to simulate plane Poiseuille flow using Molecular Dynamics? [closed]
I want to simulate 2D plane Poiseuille flow using molecular dynamics (velocity verlet algorithm) but not able to understand exactly to how to do this. Boundary condition is fine, I am confused about ...
5
votes
3answers
189 views
Why are large speaker cones required to to produce loud low frequency sounds?
Is there any reason for why a small speaker cone cannot produce low end sound at a comparable volume to higher frequencies?
I can understand how a larger speaker would be in contact with more air and ...
1
vote
1answer
39 views
The actual mass of a particle in coarse-grained molecular dynamics
If I use Lennard-Jones unit with the fix langevin command, and set both the mass and damping parameter as 1, does it mean the actual mass of a particle in this ...
0
votes
2answers
49 views
Basis Functions for Hartree Fock, and Configuration Interaction
I'm about halfway through the book Szabo and Ostlund, and while I think I understand the rough idea of Hartree-Fock and configuration interaction, there is something I would like to clarify.
For one, ...
1
vote
0answers
23 views
Probability density of reactions coordinates (collective variables)
I'm reading Chapter 8 of Statistical Mechanics: Theory and Molecular Simulations by M.E. Tuckerman. I have some difficulties understanding one formula (8.6.4).
... If these reaction coordinates are ...
0
votes
1answer
40 views
How accurate is it to use 12-6 LJ potential for interaction between nano-particle and Hydrogen molecule in LAMMPS?
I am trying to simulate a large system containing nano particles (that are fixed in space) and gas molecules passing through the void space between nano particles using LAMMPS. The nano particles have ...
2
votes
0answers
36 views
Stability criterion for leapfrog in relativistic physics
I am doing a 2D MD simulations of charge carriers in graphene using the Leapfrog algorithm. I am trying to prove that, in some specific cases (when distance between particles is small), the method is ...
1
vote
1answer
64 views
How is atomic position expressed in QM?
I am trying to understand how DFT works. I understand how to express the position of an atom or molecule in terms of the positions of the nuclei and electrons by setting up a Hamiltonian expressed in ...
0
votes
1answer
71 views
Can Einstein relation be used to calculate mobility under equilibrium dynamics?
In weak field non-equilibrium dynamics, mobility can be calculated by
Einstein relation $\mu=\frac{eD}{K_BT}$, where $D$ is diffusion constant.
Mobility can also be calculated by the definition $\mu=...
0
votes
1answer
73 views
Screening of a coulomb-like potential
Imagine that we have a potential in the form of: $U(r) \propto \frac{1}{r^n}$ in a 2D system, with the high concentration of particles interacting with the above potential. How do you find the ...
0
votes
1answer
40 views
What would happen to a liquid's pressure if interaction between molecules ceased to exist?
If a gas is composed of molecules who attract eachother, then its pressure would increase were the interactions to suddenly disappear. This can be quantitatively and qualitatively discussed using Van ...
1
vote
2answers
120 views
Series expansion of $N$-particle potential energy
I am trying to understand the so-called Taylor expansion (or series expansion) of potential energy of a system of $N$-particles. This expanded form is stated without derivation in some molecular ...
-1
votes
2answers
348 views
Where do the Lennard-Jones dimensionless/reduced units come from?
I'm a little bit confused as to where the expressions for the Lennard-Jones Potential Dimensionless units shown in this Wikipedia chart come from. I know they're derived from the L-J force equation ...
1
vote
2answers
70 views
Multiparticle simulation and Velocity Verlet Algorithm
The Velocity Verlet algorithm requires using an updated particle acceleration to compute and updated velocity. If that acceleration depends on a force that depends on distance to the other particles, ...
1
vote
0answers
25 views
Looking For a Relativistic Probability Distribution for Rotational Velocities of polyatomic molecules
I've been trying to find a suitable probability distribution function for the rotational velocity of molecules around T = 300K. It doesn't need to be incorporate QM effects, though I don't mind if it ...
0
votes
0answers
70 views
What is the difference between density functional theory and ab initio molecular dynamics?
I feel like I should know the answer to this question. But in standard implementations of (say) plane-wave DFT in softwares like VASP, the atomic positions are moved based on the Hellman-Feynman ...
2
votes
1answer
55 views
What are phonon frequencies in solids? How are they related to the interaction potentials between the constituent atoms?
I was reading a paper on self-assembly of colloidal structures, where it was mentioned that only solids with real phonon frequencies are mechanically stable. And the authors go on to manipulate the ...
0
votes
0answers
48 views
Venturi effect on molecular level
Is there a good explanation why the pressure becomes lower on the narrow part of the venturi pipe? I'm not interested in the newton explanation or pressure differences explanation. I want to ...
1
vote
1answer
62 views
Why does using deuterium mass for hydrogen improve convergence of molecular dynamics simulations of water?
I've come across many papers performing ab initio MD (Carr-Parinello or Born-Oppenheimmer) simulations of water that use the deuterium mass for hydrogen. And they state that this helps improve ...
0
votes
1answer
47 views
How do we take temperature into account in Ab-initio molecular dynamics simulation?
In Ab-initio molecular dynamics simulations, we use Ab-initio methods for calculating the ground state electronic energies of the atomic configurations visited along the dynamics. The atomic forces ...
1
vote
0answers
35 views
What type of potential is suitable for ion bombardment in Molecular Dynamics?
I would like to study ion bombardment on targets with molecular dynamics, especially on oxides. So far I ran conclusive tests with Lennard-Jones potentials, but I would like to obtain better ...
0
votes
1answer
25 views
Keeping the electronic configuration in the ground state is expensive in Ab-initio MD?
In E. Sandré & A. Pasturel's An Introduction to Ab-Initio Molecular Dynamics Schemes
If using small time steps (typically in the order of a few tenth of femto-second), the changes in the ...
0
votes
0answers
11 views
Photoreactivity/photofragmentation dependence on pressure
Most of the photofragmentation studies I see are done in vacuum or lower pressure. Is this just because of the experimental limitations or the photofragmentation doesn't matter the surrounding ...
1
vote
1answer
41 views
Energy differentiation with cut-off function
I am a new learner of molecular dynamics (MD) simulations methods and has a simple question regarding handling of cutoff functions. In MD, pairwise energy between two atoms is assumed to be a function,...
5
votes
2answers
296 views
How can I include variable particle number in a Brownian dynamics simulation?
I programmed a Brownian dynamics simulation in two dimensions.
(Coarse-grained proteins on surfaces with interaction potentials i.e. patchy particles.) Now I want to allow particles to leave or enter ...
1
vote
1answer
116 views
Linear momentum conservation for interaction between rigid body and point mass
Let's say I have an interaction potential between a rigid body and a point mass expressed in spherical coordinate : $V=V(r,\theta, \phi)$. The coordinates $r, \theta$ and $\phi$ specify the position ...
1
vote
0answers
54 views
In Monte Carlo integration for Molecular dynamics simulation, why is a Boltzmann distribution assumed?
In statistical physics, The calculation of partition function for an ensemble takes a Boltzmann's distribution of the Hamiltonian. Similarly, In Monte-Carlo integration of Molecular Dynamics ...
0
votes
1answer
132 views
Body Rotation in a Molecular Dynamics Simulation
I have been trying to simulate particles trapped in a parabolic potential in two dimensions. Due to the circular symmetry of the system, in the ground state at zero temperature, the particles are seen ...
0
votes
0answers
14 views
Coordinates of all the atoms in protein molecule for the given Ramachandran angles for all the peptides
How to determine coordinates of all the atoms when ramachandran angles are given ? Can someone suggest some references to determine all the coordinates for the given Ramachandran angles ?
0
votes
1answer
238 views
Specific heat capacity at constant pressure formula
I want to calculate specific heat capacity at constant pressure for a single walled carbon nanotube by using of fluctuation in enthalpy. The fluctuations were obtained from molecular dynamics ...
2
votes
1answer
104 views
What is water pressure, really? [duplicate]
It's easy for me to imagine gas pressure on a molecular level. More pressure means that more molecule bounce against the thing you are measuring, or the molecules hit it with more speed or the ...
1
vote
0answers
38 views
Generalized reaction rate for elementary process
Most textbooks give the reaction rate
$$r = k [\mathrm{R}_1]^{a_1}[\mathrm{R}_2]^{a_2} \tag{1}$$
for the elementary process $a_1 \mathrm{R}_1 + a_2 \mathrm{R}_2 \rightarrow \mathrm{P}$. However, ...
0
votes
1answer
249 views
When do gas molecules deviate from Maxwell Boltzmann distribution?
The velocity of the gas molecules at room temperature obey Maxwell Boltzmann distribution. When we say velocity, the distribution is true for each component right ? means vx, vy and vz are in MB ...
2
votes
1answer
379 views
Normal modes: how to get reduced masses from displacement vectors, atomic masses and vibrational frequencies
I'm calculating normal vibrational modes in a large molecular system. My goal is to obtain, for each normal mode, the vibrational frequency, the list of displacement vectors and the reduced mass.
I'...
0
votes
1answer
82 views
Pair correlation function vs Bond length distribution of a van der Waal dimer
For a weakly bonded molecular dimer (when two atoms are interacting through van der Waal (vdW) interaction). Do the distribution of pair correlation function and vibrationally average bond-length ...
0
votes
0answers
45 views
Quantifying physical intuition about heat and motion
Assume that we are in deep space. There are two objects Orange and Blue. Initially, Orange is at a temperature of 200K and Blue is at 1000K. Consider the following scenarios. For now assume that there ...
1
vote
0answers
41 views
What is the narrowest possible functioning straw that could be made?
Let's assume that the straw/pipe/tube can be made of any material, but it should be at least 100 times as long as the inside is wide.
How narrow could the inside of the straw be made before it is no ...
0
votes
1answer
188 views
How to get the phase transition diagram for a coexistence phase simulation?
I am running a lammps program to get the phase transition diagram. one for gold and the other for silicon. I am measuring the melting point by investigating the growth of each phase at different ...
