As i know to determine cut-off energy, charge leakage must be considered.But we can also control charge leakage by altering muffin tin radius. Now is there any rule, or criteria to calculate cut-off energy?
As far as I understand your problem, you would like to determine an proper cutoff value to be used in your simulations. The general approach is to run a series of single-point simulations of the same model (the same geometry and other parameters e.g. functional) and plot total energy vs cutoff. The reasonable choice is where the energy does not change significantly. Too large cutoff will slow down your calculations rapidly, while too low values will generate useless energy values (in extreme cases also geometry disorders).
The cut-off energy is taken by default -6 eV in Wien2k package
I believe that the basis set cutoff parameter in Wien2K is the parameter known as "RKmax", the product of the smallest muffin-tin radius and the magnitude of the largest k-vector. This is a dimensionless quantity, suitable values typically fall in the range 6 to 9 for a LAPW+local orbitals calculation. To determine what is a suitable value, see the answer by Daniel Smykowski.
http://www.wien2k.at/lapw/
Dear Amir,
Dr. Björkman is right. The cut-off parameters to expand basis functions in wien2k is determined by RMTKmax (usually between 5-9).
So, to achieve correct calculations, you should optimize this parameter as follow.
The Dr. Smykowski description is about separating energy between valence and core states to determine core, semicore and valence states, no cut-off energy.
Hello,
Answer from WIEN2k FAQ:
What is the cutoff energy? Is -6.0 Ry (Wien's default) always a good?
A. (GS) In Wien2K, electrons are treated either as valence electrons or core electrons. Core electrons are assumed to not interact. The -6.0 Ry in Wien2K specifies the energy below which states are treated as core states. It is a relative energy (wrt to Energy = 0 Ry used in Wien2K, which is arbitrary). What is NOT arbitrary is the energy of typical valence states, which are approximately in the range -1 Ry … +1 Ry. The specific value of -6 Ry comes from experience and there is almost never a reason to change it. Usually the division between core and valence states can be done by looking at the periodic table. For example Ti has an electronic configuration of 1s2 2s2 2p6 3s2 3p6 4s2 3d2 = [Ar] 4s2 3d2, where [Ar] specifies the closed electrons shells of Argon. The electrons in closed shells are usually treated as core electrons. However, for certain atoms, some of electrons in a closed shell are sufficiently delocalized that they do interact with the valence electrons and treating them as core electrons introduces an unacceptable error. For example, this is the case for the Ti 3p6 states. In Wien2k, the energy cutoff of -6 Ry relative to typical valence state energies of -1 Ry … 1 Ry is used an indicator that enough interaction between electron states takes place to warrant treating them ALL as valence electrons.
to Original text follow this link http://physics.oregonstate.edu/~minote/COURSES/ph575/doku.php?id=wiki:wien2k_faq
Dear Jaafar sir,
1. please provide the reference for attached figure (relative energy versus RKmax).
2.please discuss how to select RKmax range (like 5-9 or 7-11) for any compound/material like BaTiO3.
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