Hi, Shahzad!

In VASP, the order in which you calculate properties can depend on your specific research goals and the system you are studying. However, there is a common sequence of calculations that is often followed in electronic structure calculations using VASP. Here's a general order in which properties are typically calculated:

1. Geometry Optimization: Before calculating any electronic properties, it's essential to optimize the atomic positions to find the most stable atomic configuration. This involves minimizing the total energy with respect to atomic positions until the forces on the atoms are sufficiently small.

2. Electronic Structure: Once you have an optimized geometry, you can calculate various electronic structure properties:

2.1. Electronic Density of States (DOS): This provides information about the distribution of electronic states in your system.

2.2. Band Structure: To study the electronic band structure, which helps in understanding the electronic band gap and the nature of bands (e.g., valence and conduction bands).

2.3. Charge Density: To visualize the charge distribution in your system.

Mulliken Population Analysis: To understand how electrons are distributed among atoms in your system.

3. Magnetic Properties: If your system has magnetic atoms or moments, you may want to calculate:

3.1. Magnetic Moments: The magnetic moments of individual atoms or the total magnetic moment of the unit cell.

3.2. Magnetic Ordering: To determine the preferred magnetic ordering (ferromagnetic, antiferromagnetic, etc.).

4. Thermodynamic Properties:

4.1. Formation Energy: If you're interested in the stability of compounds, you can calculate their formation energies.

4.2. Entropy: To estimate the thermodynamic properties at finite temperature.

5. Mechanical Properties:

5.1. Elastic Constants: To determine the mechanical stability and elastic properties of materials.

5.2. Bulk Modulus: A measure of the material's response to uniform pressure.

6. Chemical Reactivity:

6.1. Chemical Potential: To understand the reactivity of your system with respect to external conditions (e.g., chemical potential of electrons or atoms).

7. Optical Properties:

7.1. Dielectric Function: To study the optical properties, including absorption spectra and refractive index.

8. Thermal Properties:

8.1. Phonon Dispersion: To investigate the vibrational properties and thermal conductivity.

8.2. Thermal Expansion: To understand how the lattice parameters change with temperature.

The order in which you perform these calculations can vary depending on your specific research goals. For example, if you are interested in the electronic structure of a material, you may focus on DOS and band structure early in your workflow. If you are studying a reaction pathway, you might start with geometry optimization and then move on to reaction energetics.

Always consider the specific properties that are most relevant to your research question and adjust your workflow accordingly. Additionally, keep in mind that some properties may require more computational resources and longer simulation times than others.

For a DFT calculation, the standard procedure is that you perform a geometry optimization of the lattice parameters and the atoms positions. Then you perform a self-consistent calculation using the CONTCAR file that was generated during relaxation. The self-consistent calculation will generate a CHGCAR file which you should use as the starting point for your next calculations that include DOS, bandstructure, optical properties and thermoelectric properties. That's the overall order you would use for any arbitrary DFT calculation and the answer by Mudassir Ishfaq is very complete in regard to how you approach the problem. However, since you mention 2D magnets specifically I will address that in more detail below.

You have to be very careful when you deal with 2D magnets. The first consideration here, in the simplest case of a collinear spin polarized system, is that you have to decide based on whether you are interested on how to initialize the magnetic moment. A quick rule of thumb is to over estimate the magnetic moment for the d-shell atoms by assigning to a integer that is slightly greater than the number of unpaired electrons while keeping the magnetic of other atoms to around 0.5 Bohr Magnetons. You may also consider DFT+U depending on your system during relaxation. You can also relax the system first without a U value then adjust and relax again once you have a handle on which U value you should be using for your system based on experimental values, other DFT studies on the same material and the properties of your system. You may also look into using linear response for this as shown in these 2 examples:

https://www.vasp.at/wiki/index.php/Calculate_U_for_LSDA%2BU

http://hjkgrp.mit.edu/tutorials/2011-05-31-calculating-hubbard-u/

For magnetic systems in general, you may have to switch of the symmetry depending on your system (using the ISYM tag). The other important note is that for monolayer systems, you should make the layer images as far away as possible (I usually use 35 angstroms at the beginning of the relaxation) if I am using ISIF = 3 to relax both the cell and the atoms positions. This is because VASP will try to shrink your lattice parameters along the z-axis and if you start with say 15 Angstroms between the layers, you may end up with the layers getting close to each other to the point where they can interact with each other. Using a larger vacuum makes the computation more expensive, so typically run ISIF = 3 on looser setting such as EDIFF = 1E-6 or 1E-5 and EDIFFG = -2E-2 or EDIFFG = -1E-1 then run ISIF = 2 with stricter settings and a smaller vacuum distance. There is a fix for this but you have to recompile vasp to include it. Find more info here:

https://github.com/Chengcheng-Xiao/VASP_OPT_AXIS

After relaxation you can then proceed with a self consistent calculation from which you get a CHGCAR that you can use to start your DOS, bandstructure, optical and thermal properties calculations. For optics, I will point you towards two answers in which some of the important considerations for calculating optical properties are covered

https://www.researchgate.net/post/How_to_calculate_Plasma_Frequency_using_VASP

https://www.researchgate.net/post/How_can_we_get_optical_properties_using_vasp_code

Hope you find this helpful!

Sir Mudassir Ishfaq thanks

Mudassir Ishfaq Ahmed Elrashidy

After self-consistent calculation how we can knows that our calculation going well?

Strictly computationally speaking, a good self-consistent calculation is one that is well-converged. This means that the energy difference criterion you use should be small (optimally less than or around 10^-6 or less). That's the first way to check for convergence. The second, and most important, is the total energy and the different properties you predict should also be well-converged within reason regardless of how you change your energy cutoff and your k-mesh. In fact, you should make an informed decision about parameters for subsequent calculations based on convergence in terms of tuning the parameters above.

Practically speaking, the first thing you should look into is experimental work if it exists. If you're working with 2D magnetic materials, one of the first places you may want to check is the reported magnetic moment. Even in the cases you do not know the experimental values, you should be able to see close values to what you expect from your system. Is what you got consistent with the electronic configuration, is it more or less consistent with Hund's rule if that's relevant to your material?

Secondly, if data from other DFT calculations exists, you should compare the results with other works and reason about it.