15
votes
On the nature of zero-point energy (ZPE)
In the Born-Oppenheimer approximation nuclei are assumed to behave as classical point-like particles. However, in reality the wave-particle duality also applies to them, and so the Schrödinger ...
- 17.6k
14
votes
Converting adsorption binding energy to absolute temperature
If I want to break a Li$_2$ molecule (i.e. remove atom A from atom B), one way to do it is by shining a laser on it such that the frequency ($\nu$) or energy ($h\nu$) corresponds to the difference ...
- 33.1k
10
votes
LAMMPS: Why does the NVT fix vary in temprature step-by-step even though I am giving an initial and final temp of 1500K?
The instantaneous temperature will almost always fall to half of its original value when thermal equilibrium is established when we attribute velocities to the atoms in a crystal.
The equipartition ...
- 3,846
9
votes
LAMMPS: Why does the NVT fix vary in temprature step-by-step even though I am giving an initial and final temp of 1500K?
As a consequence of these commands:
fix 1 all nvt temp 1500.0 1500.0 100
timestep 0.001
you are running your system with a Nose-Hoover thermostat whose time ...
- 2,498
8
votes
How to calculate temperature dependent phonon band structure in VASP
There are two main contributions that can be included in the DFT context when calculating phonons at finite temperature:
Thermal expansion. As temperature increases, the volume of materials changes (...
- 10.9k
8
votes
Converting adsorption binding energy to absolute temperature
A more approximate but sometimes easier approach than the one of Nike Dattani might be to calculate an artificial reaction coordinate of separating the two systems. This can be done manually or by ...
- 601
7
votes
How to simulate atomic scattering from solid walls at finite temperature for a particles in a box simulation?
Whatever scattering mechanism you choose must respect detailed balance in equilibrium: on average, the number of particles hitting a patch of the wall at a given angle and velocity must equal the ...
- 171
5
votes
How to simulate atomic scattering from solid walls at finite temperature for a particles in a box simulation?
Since no one has responded with expertise, I'll attempt a speculative answer here.
To my mind, the simplest model of the atoms on the surface of the walls would be an ensemble of independent ...
- 6,569
5
votes
Temperature effect on elastic constant using VASP
It is always better to write your own code to get elastic constants. For example , In case of cubic system, we need three types of distorsion to unit cell. Now elastic constant is simply slope of ...
- 3,846
5
votes
Is there an upper limit of temperature after which the quasi-harmonic approximation (QHA) fails?
The starting point of most calculations is the Born-Oppenheimer approximation, which separates the electronic and nuclear degrees of freedom. The electronic structure problem is then solved using a ...
- 10.9k
5
votes
Reaction rate estimation for relatively complex reactions
Relatively big systems can be treated with fragmentation methods that allow one to reduce the cost of the overall computation by using the most accurate and/or expensive approach on the most relevant ...
4
votes
In which theoretical framework does the size of an atom depend on the temperature of the gas (Bose-Einstein condensates)
In calculations of the electronic energy/wavefunction, temperature typically is not taken in to account (besides cases of orbital occupation smearing, though this is used more as a computational trick ...
- 15k
3
votes
How to calculate temperature dependent phonon band structure in VASP
You can try the library TDEP, which has an example to calculate Phonons dispersions as a function of temperature.
3
votes
On the nature of zero-point energy (ZPE)
The Born-Oppenheimer (BO) approximation works well at high temperatures (far from 0 K), but the quantum nature of the nuclei (i.e. the zero-point energy) is an important consideration at low ...
- 6,569
2
votes
Does the thermal evolution of molecular structures critically affect the validity of the calculated magnetic anisotropy?
Not always the research pipeline is from experimental to theory. The group of Professor Artem Oganov had very interesting results where they started predicting theoretical structures (at extreme ...
- 22k
2
votes
Temperature effect on elastic constant using VASP
The following paper is quite nice, in my opinion:
Shang et al., Temperature-dependent elastic stiffness constants of α- and θ-Al2O3 from first-principles calculations, J. Phys. Condens. Matter 22 (...
- 1,718
1
vote
How is temperature changes implemented in a molecular dynamics simulation?
"It's done with a thermostat in the same way a constant temperature simulation is performed. It's just that in simulated annealing, the target temperature varies over some schedule. Here is a ...
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