Micro Flashcards
(29 cards)
What are the four particle methods in microscopic scale?
Molecular Dynamics (MD)
Non-Equilibrium Molecular Dynamics (NEMD)
Monte Carlo (MC)
Direct Simulation Monte-Carlo (DSMC)
In Molecular Dynamics, which equation are the interacting particles’ position and velocity based on? (MD)
Newton’s equation of motion
F = m a
What are the physical range of particle methods in Microscopic scale?
Atoms
What are the two possible statistical distribution in Molecular Dynamics? (MD)
Micro-canonical (NVE) -> constant energy and volume
Canonical (NVT) -> constant temperature and volume
What are the range of applications of Molecular Dynamics? (MD)
simulation of the following:
-liquid properties
-defects in solids
-fracture processes
-friciton and lubrication
-biomolecules
-electronic properties of materials
In Molecular Dynamics, what is the inter-atomic potentials? (MD)
It describes the forces between interacting particles/atoms, defining how they interact based on distance
*an example is the Lennard-Jones and Coulomb potentials
In Molecular Dynamics, what is the pairwise-potentials? (MD)
It is an inter-atomic potentials ONLY between two bodies
When is the Lennard-Jones potential usually implemented? (MD)
and when is it not?
Usually used in modelling closed shells systems and fluid modelling
Not used in Open SHells and systems characterised by delocalised electrons
Describe the equation of motion for Molecular Dynamics (MD)
Total Force on particle i = sum of N-1 pair-forces
Particle Velocity = change in position wrt. time
Momentum = Velocity * Mass
Force = change in Momentum wrt. time
Which type of integration algorithms can we use to define velocities and positions of the particles in Molecular Dynamics? (MD)
Euler algorithms (first order accurate)
Velocity-Verlet algorithm(2nd order accurate)
Why is a cut-off radius used? (MD)
Because Lennad-Jones potentials have infinite range with complexity of O(N^b) with b being the number of particles/atoms
What do we do at the periodic boundaries of the domain? (MD)
we interact the particles in the primary box with their images
Why is the Linked-list-cell algorithm used? (MD)
Due to the neighbour searching issue where the contribution of every particle in the main box causes a complexity of O(N^2)
*Linked-list-algorithm has a complexity of O(N)
*It is the most popular method in Molecular Dynamics
in Molecular Dynamics, what are the three initial positions on a lattice? (MD)
Simple Cubic(SC)
Body Centered Cubic(BCC)
Face Centered Cubic(FCC)
How can we define/setup the initial velocities? (MD)
assume it to be zero
take it from a Maxwellian distribution
Random
What is the metastable state? (MD)
It is when a system is at an non-global equilibrium state
*caused by a too low initial kinetic energy
What are the two ways of starting a Molecular Dynamic simulation? (MD)
using initial randomisation(Temperature and/or initial lattice position)
continuing a simulation/using a previous run’s final steady state configuration
What are the four basic macroscopic quantities (MD)
Potential Energy
Kinetic Energy
Total Energy
Temperature
What does the Virial theorem describe? (MD)
The relation between the average over time of the total kinetic energy to that of the potential energy
How does the Mean Square Displacement behave for different states of matter? (MD)
solid : MSD saturates to a finite value
fluid : MSD grows linearly in time
in Radial Distribution Function, how does the g(r) determine the state of matter? (MD)
solid : g(r) has pronounced peaks around the lattice of a given atom
liquid : g(r) has a major peak close to the average atomic distance
gaseous : g(r) zero at a short distance
What does the Radial Distribution Function describe? (MD)
how particle density varies as a function of distance from a reference particle
What is the difference between Monte-Carlo and Direct Simulation Monte Carlo? (DSMC & MC)
Monter-Carlo is a static method, while DSMC is dynamic
How does the Monte-Carlo algorithm work?(MC)
1) random move of a particle
2) calculate the difference of total energy if the move is realised
3.1) move is allowed if energy decreases
3.2) move is allowed if energy increases with a probability
