Hello Shaira,

for charge density difference graphs the incar settings are not that specific, of course, the settings will influence the accuracy, so the choices should be tested, the settings for algo and prec given above are usually good choices, but you can just run some test calculations to see the effects

for ismear and sigma, these should be chosen according to the system that you are investigating, for static calculations tetrahedron method with Blochl correction is usually a good choice (for some guidance see http://cms.mpi.univie.ac.at/vasp/vasp/ISMEAR_SIGMA_FERWE_FERDO_SMEARINGS_tag.html)

ADDGRID, LASPH, and IDIPOL are often not necessary, but this again depends on the system, idipol if you want to do dipole corrections which can be needed if you have got, for example, a polar surface, lasph can be a good idea for certain systems such as f and 3d elements or when methods such as lda+u or hybrid functionals are used, addgrid adds an additional support grid for the evaluation of the augmentation charges

for Bader analysis  you have to set the flag LAECHG= .TRUE. to produce the following files: the core charge is written to AECCAR0 and the valance charge to AECCAR2, which have to be summed to obtain the complete info on the charge in one file (see e.g. http://theory.cm.utexas.edu/henkelman/code/bader/), here the FFT mesh should be chosen carefully via the NGXF, NGYF, NGZF tags, as far as I know the addgrid setting can produce problems within the bader analysis, so I would not use that but check convergence via the NGXF... tags

hope this helps

cheers

gregor

Hello Gregor,

Thank you very much for the comprehensive answer. This surely helps.

Best,

Shaira

For bader charge analysis, you can see:

http://theory.cm.utexas.edu/henkelman/code/bader/

You can just set the tag: LAECHG=.TRUE.

LCHARG=.TRUE.

Thank you Jian for your answer.

Be careful of "ADDGRID = .TRUE." added in INCAR for the Bader charge analysis. It may produce unexpected results especially for the use of Henkelman et al. integration method (bader tool, http://theory.cm.utexas.edu/henkelman/code/bader/) in Bader charge analysis.

http://theory.cm.utexas.edu/forum/viewtopic.php?t=1469

I have experienced a similar problem. I used alternative tool named "Critic2" (http://schooner.chem.dal.ca/wiki/Critic2), which implements both Henkelman et al. integration method and Yu-Trinkle integration method. The Yu-Trinkle integration method in Critic2 tool gave reasonable results for Bader charge analysis, but the Henkelman et al. integration method in Critic2 and bader tools doesn't.

Hi Zhufeng,

Thank you for the info regarding the addgrid. I'll check the resource you posted. May I ask how did you figure out that Critic2 gives more reasonable result than bader tools for your system? If the two methods give different results, how do you decide which is the correct bader charge result?

Best,

Shaira

Hi, Shaira

For the symmetry-equivalent atomic sites, the atomic volumes (charges) should be close to each other or nearly equal.

For example:

In the following example, atom sites 1 and 2 are symmetry-equivalent.

1) Results obtained with using "ADDGRID = .TRUE."

# X Y Z CHARGE MIN DIST ATOMIC VOL

--------------------------------------------------------------------------------

1 2.1079 -1.2170 5.8729 9.2140 1.0826 12.6819

2 0.0000 2.4339 5.8729 9.2150 1.0826 12.6847

2) Results obtained with using "ADDGRID = .TRUE."

# X Y Z CHARGE MIN DIST ATOMIC VOL

--------------------------------------------------------------------------------

1 2.1079 -1.2170 5.8729 9.7757 0.6999 14.2575

2 0.0000 2.4339 5.8729 9.4710 0.7757 13.0788

Hi Zhufeng,

Thanks for the answer. I also noticed that when I added ADDGRID=.TRUE. I get errors when running the Bader program.

I decided to remove it from INCAR and use thrice the values of  NG?F tags that I used in calculating the correct  energy.

Thanks for the help.

Shaira

Hi,

Besides the Bader analysis mentioned in your question, you could perform DDEC6 analysis to compute the net atomic charges and bond orders. This method has a lot of useful properties. See the following papers for details:

(1) T. A. Manz and N. Gabaldon Limas, “Introducing DDEC6 atomic population analysis: part 1. Charge partitioning theory and methodology,” RSC Advances, 6 (2016) 47771-47801 (http://dx.doi.org/10.1039/C6RA04656H).

(2) N. Gabaldon Limas and T. A. Manz, “Introducing DDEC6 atomic population analysis: part 2. Computed results for a wide range of periodic and nonperiodic materials,” RSC Advances, 6 (2016) 45727-45747 (http://dx.doi.org/10.1039/C6RA05507A).

(3) T. A. Manz, "Introducing DDEC6 atomic population analysis: part 3. Comprehensive method to compute bond orders," RSC Advances, 7 (2017) 45552-45581 (http://dx.doi.org/10.1039/C7RA07400J ). (open access)

The DDEC6 method is available in the free Chargemol program (http://ddec.sourceforge.net) which can analyze the outputs of VASP, Gaussian, and other quantum chemistry programs.

For VASP, follow these steps:

(1) Get your desired geometry from either experiments or geometry optimization or any other method of your choice.

(2) Prepare an INCAR file with the following keywords: NSW = 0 (don't change geometry), Prec = Accurate (use an accurate integration grid), ENCUT = value greater than or equal to 400 eV, LAECHG = .TRUE. (generate the AECCAR0 and AECCAR2 files), and LCHARG = .TRUE. (generate the CHGCAR file), and any other keywords appropriate to your particular material calculation.

(3) In the KPOINTS file, set up your k-point grid so that the product of number of k-points along each lattice direction times the length of that lattice vector is at least 16 angstroms. For example, if your lattice vector lengths are 2.54 angstroms, 5.8 angstroms, and 17.2 angstroms, you could use a 7 (or 8) x 3 x 1 kpoint mesh. Usually the auto Monkhorst-Pack scheme works well; however, use Gamma point if k-point mesh is 1 x 1 x 1.

(4) Place the AECCAR0, AECCAR2, CHGCAR, and POTCAR file into a directory and add the job_control.txt file. (See above program manual for how to set up and use the job_control.txt file.)

(5) Run the Chargemol program to produce the output files containing the net atomic charges, atomic spin moments (for magnetic materials), atomic dipoles and quadrupoles, bond orders, overlap populations, etc.

Dear Prof Thomas A. Manz,

Thank you for the info regarding.

Sometime charges are not properly converged, then one must use the finer grid points by using VASP INCAR tags, NGXF, NGYF and NGZF. The default values are printed in the OUTCAR file.

Hi,

The step by step procedure to perform the Bader charge analysis using VASP and charge density difference plot using VESTA is clearly explained in a Youtube channel. You can find it here:

https://www.youtube.com/watch?v=UxPrN7KcswA

https://bit.ly/2UtvbHE

Best,

Rasoul