Rwigs and Lorbit (1)

Rwigs and Lorbit are two parameters related to the density of local states or to the projected state densities; Rwigs refers to the Wigner–seitz radius,lorbit in front of the LO refers to the local.

These two parameters play a decisive role in the analysis of the local orbit, and the following is a summary of the 1999 nature:

P. Strange, A. Svane, W. M. Temmerman, Z. Szotek & H. winter,understanding the valency of rare earths fromFirst-principles theory,nature399,756-758( -June1999) | Doi10.1038/21595. The rare-earth Metals has a high magnetic moments and a diverse range of magnetic structures1. Their magnetic properties is determined by the occupancy of the strongly localized 4f electronic shells, whileThe outer s–d electrons determine the bonding and other electronic properties2. Most of the Rare-earth atoms is divalent, but generally become trivalentinchThe metallic state. In some materials, the energy difference between these valence states isSmall and, by changing some external parameter (such aspressure), a transition fromOne to the other occurs. But the mechanism underlying ThisTransition and the reason forThe differing valence states is not a well understood. Here we report first-principles Electronic-structure calculations that enable us to determine both the valency and the LAT Tice size asA function of atomic number, and hence understand the valence transitions. We find that there is types of F electrons:localized core-like f electrons that determine the valency, and Delocaliz Ed Band-like F electrons that is formed through hybridization with the S–D bands and which participateinchBonding. The latter is found onlyinchThe trivalent systems;ifTheir number exceeds a certain threshold, it becomes energetically favourable forThese electrons to localize, causing a transition to a divalent ground state.

Rwigs and Lorbit 3 parts share a little experience of the monk (if you have any objection, please leave a message to explain the problem clearly, and discuss). Rwigs and Lorbit (1) are settings about Rwigs. The definition of rwigs is found in Wikipedia: The Wigner–seitz radius, named after Eugene Wigner and Frederick Seitz, is the radius of a sphere whos E volume is equal to the mean volume per atom in a solid.         This parameter was used frequently in condensed matter physics to describe the density of a system. Rwigs can be found in the Potcar file in vasp:

Rwigs = 2.330; Rwigs = 1.233 Wigner-seitz radius (au A)

                 Three points in:        (1) units: 2.33 is in Bohr units, and 1.233 is a unit, this conversion as long as a few seconds, please do a conversion. Incar inside is a unit, so should take 1.233.           (2) method: When calculating the block (bulk), it is feasible to take the potcar directly and to take the value according to the volume ratio in the Outcar, that is, the vasp manual explicitly mentions [3]: 

 as  Do  is inch The spirit of atomic sphere calculations. VASP writes a                                    line198.5 %.

Online there is a better reprint about the Rwigs, the original post from Chinaunix's author Beyondstar[4]:

--------------------------------------------------------------------------------------------------------------- ---When using vasp to calculate the density of the state, the use of lorbit=1 is, the need to manually set Rwigs, in the Incar Rwigs is a unit of a, add the appropriate rwigs radius, so that the volume obtained by the rwigs is approximately equal to the entire volume, This time the rwigs radius is set most correctly. V = 4/3 * pi * (sum [n_i * rwig_i^3])According to the above formula, you can calculate the size of the system using the ball approximation, the ratio of this volume to the real volume of the system can be found from the Outcar, using the command grep% Ourcar, you can get this percentage; so we know volume V, atomic number N,    According to the above formula can directly find Rwigs, fill in Incar. If you want to calculate pdos, or need the charge amount and magnetic moment of each atom, you can set
1. Paw case, Lorbit >10, at this time no rwigs, here npar not equal to 1, should also be able to get pdos and so on.
2. If Lorbit is less than 10, to get PDOs, the NPAR is set to 1 when calculating.
Lorbit and Rwigs settings, see vasp Manual (if reproduced please indicate the source). --------------------------------------------------------------------------------------------------------------- ----in Beyondstar's Bolg, someone said: "Different kinds of atoms rwigs radius, if there are several kinds of atoms in a cell, how one by one to determine the rwigs radius of various atoms?" The above formula is a condition, but the condition is not enough ah? "In fact, this question is explicitly given in the VASP Handbook:

For binary Systems There isNo unambiguous to define rwigs and several choices is possible. In all cases, the sum of the volume of the spheres should is close to the total volume of the cell (i.e the sum of the Val UEs given by VASP should be around -%. ①one Possible Choice isToSetRwigs such that the overlap between the spheres isMinimized.②howeverinchMost cases, it isSimpler to choose the radius of each sphere such that they is close to the covalent radius asTabulatedinchMost periodic tables. This simple criterion can usedinchMost cases, and it relies at least on some "physical intuition".

(3) Scope of application: Rwigs is used only for the block, and for the current field of DFT active in two-dimensional crystals and one-dimensional nanotubes, it is not possible to use "volumetric method" to determine the value of the parameters. Reason: ① for a two-dimensional or one-dimensional system contains a vacuum layer; ② Two-dimensional or one-dimensional system is different from the physical nature of the block.           Practice: ① Debugging Method: By adjusting the rwigs to the literature with the state density (need to compare with the PR series of DfT literature, a higher degree of feasibility) to be compared and then to determine; ② Empirical method: Empirically judge whether Rwigs is reasonable according to the two-dimensional or one-dimensional molecular or atomic orbital morphology. "1" Wigner–seitz Radius:http://en.wikipedia.org/wiki/wigner%e2%80%93seitz_radius "2" Wigner–Seitz cell:http:// En.wikipedia.org/wiki/wigner%e2%80%93seitz_cell "3" Rwigs (vasp manual): http://cms.mpi.univie.ac.at/vasp/vasp/ Rwigs.html "4" vasp calculate the density of the Rwigs method (original): Http://blog.chinaunix.net/uid-7726704-id-2045192.html "5"/http Simulation.haotui.com/viewthread.php?tid=11924&extra=&page=1

Rwigs and Lorbit (1)