In this tutorial, we learn to use the OF-DFT App to compute electronic structures based on the Orbital-Free Density Functional Theory (OF-DFT). First, be sure you have installed the App from SAMSON Elements. Click on the logo to display the App window :
On the left, from top to bottom :
- The parameters of the mesh on which the electronic structure will be computed, with:
- The margin taken around the nuclei
- The spatial step.
- The parameters of the optimization method, with :
- The function that is to optimize, several versions of OF-DFT are available.
- The precision wanted for the computation of the electronic repulsion (or Hartree Potential)
- The classic parameters for a steepest descent algorithm : stopping threshold and constant step size.
- The maximum number of step of the steepest descent algorithm.
- A tool box to visualize the 3D-functions used to compute the electron density :
- The electrostatic potential, created by pseudo-atoms (nuclei + core electrons)
- The electron density.
- The electronic potential, created by valence electrons.
- A button to clear the displayer window, on the right.
Creation of the density grid
To begin, you have to create a molecular system. Due to restrictions on available proper pseudo-potentials, only 9 elements are available :
- Lithium (Li)
- Magnesium (Mg)
- Aluminum (Al)
- Silicon (Si)
- Phosphorus (P)
- Gallium (Ga)
- Arsenic (As)
- Indium (In)
- Antimony (Sb)
The application will not see other elements.
- Create a cubic face-centered crystal with the Crystal Creator App, with between 2 and 4 repetitions of the cell, depending on your computer performances.
- In the App window, choose a box expand of 15A and a mesh step size of 1A, or smaller if you are patient.
- Click on “Create Grid”
Play with the density map
In the window App and the toolbox “Grid Drawing”, select “electron density lvl1” and click “Draw density”. A new visual model appears, you can play on the threshold of the density by selecting its properties. You also can see the electric potential created by ions (“electrostatic potential”) or the one created by valence electrons (“Hartree Potential lvl1”)
Optimize the electronic density
For the optimization algorithm, the default parameters are sure. Having a bigger step size would make the method unstable very fast. Click on “Start optimization” to launch the algorithm, depending on your system, your algorithm’s parameters and your computer, it can take some time. Open other visual models to see how the electrons density has changed.
Create an interaction model running with OF-DFT.
An interaction model based on the OF-DFT is available :
- Create a system to optimize.
- Add a simulator and select “OF-DFT Interction Model” as an interaction model and “Steepest descent” as a state updater.
- In the factory window appearing, take the same parameters than before.
- Launch the simulation.