I am trying to make some calculations with CdTe. The DFT+U method is commonly used in the literature to correct for the localised Cd d-electrons. Therefore, I have attempted to do the same thing within Abinit by adding a Hubbard potential U to the Cd 4d electrons. I am using the latest PAW datasets for Cd (12 valence electrons: 4d, 5s) and Te (6 valence electrons: 5s, 5p) found in the JTH PAW atomic datasets table (https://www.abinit.org/ATOMICDATA/048-cd/index.html).
However, whenever running a calculation, I receive the following warning in the logged output every time:
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usedmft and usepawu are both activated
This is not an usual calculation:
usepawu will be put to a value >= 10:
LDA+U potential and energy will be put to zero
and this despite a DMFT calculation not being activated. In fact, I explicitly set usedmft to 0 to insure that it is not activated. See my .in input file below:
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# Crystalline cadmium-telluride: computation of the total energy(Hartee or eV)
# 1. Define physical system
#Definition of the unit cell (Bohr)
rprim 0.0 0.5 0.5 # The primitive vectors for an FCC lattic
0.5 0.0 0.5
0.5 0.5 0.0
#Definition of the atom types
ntypat 2 # There is only one type of atom
znucl 48 52 # The keyword "znucl" refers to the atomic number of the
# possible type(s) of atom. The pseudopotential(s)
# mentioned in the "files" file must correspond
# to the type(s) of atom.
#Definition of the atoms
natom 2 # There are two atoms in the unit cell
typat 1 2 # 1 Cd and 1 Te
xred # CdTe is also a Zinc-blende diamond structure
0 0 0
0.25 0.25 0.25
# 2. Calculation parameters: cut-off energy, nbands and k-grid
nband 19 # Take twice the number of filled bands i.e. 2 e's per band
kptopt 1 # Option for the automatic generation of k points, taking
# into account the symmetry
nshiftk 4 # of the reciprocal space (that form a BCC lattice !),
# repeated four times, with different shifts:
shiftk 0.5 0.5 0.5
0.5 0.0 0.0
0.0 0.5 0.0
0.0 0.0 0.5
# In cartesian coordinates, this grid is simple cubic, and
# actually corresponds to the
# so-called 4x4x4 Monkhorst-Pack grid
# Converged parameters
ngkpt 8 8 8
# DFT-U term
lpawu 2 -1
upawu 5.0 0.0 eV
jpawu 0.1 0.0 eV
# 3. Calculation parameters: self-consistent field loop
#Definition of the SCF procedure
nstep 30 # Maximal number of SCF cycles
tolvrs 1.0d-10 # tolerance used in PAW1 tutorial; for potential residual
#diemac 12.0 # Although this is not mandatory, it is often advantageous
# to precondition the SCF cycle. Here we follow the
# prescription for bulk silicon.
# 4. output
I should mention, I only began getting this warning when I upgraded my version of Abinit from 8.0.8 to 8.10.2.
Nevertheless, curiously, although the warning claims that the U potential will be set to 0 and that usepawu is set to >=10 (no idea what a value of >=10 means or does as the variable description for usepawu only describes the values 0, 1 and 2), in reality the U potential does not seem to be set to 0 (nor usepawu to >=10) as different U values still have an effect on the lattice parameter, band gap and bulk modulus. That is, when the Full localised limit (FLL) double-counting correction term is used. On the other hand, when using the Around mean field (AMF) double-counting correction term, there is indeed no significant effect of the U potential on the investigated parameters - lattice parameter, band gap, bulk modulus. See the attached figure below for a comparison of when using FLL versus AMF on the parameters as a function of U.
Furthermore, when looking at the DOS - in the case of when using FLL, the Cd 4d electron states shift as is expected. However, when using AMF, the DOS are not effected regardless of which U potential is being used.
Therefore, it seems to me that the warning message is sent regardless of if the FLL or AMF double-counting correction term is used, but that in the case of FLL nothing actually changes. However, in the case of AMF, it seems that the U potential is in fact set to 0.
I should mention that I was getting exactly the same results when using Abinit version 8.0.8, the only difference when switching to version 8.10.2 was that the warning message started appearing. Furthermore, I have done the same test with ZnO and it showed the same results in that when using FLL the U potential made a difference, but with AMF U does nothing.
Is this possibly a bug or am I missing something?