# [CP2K-user] DFT+U calculations for Cr3+ in MgCl2-KCl melts

Vyacheslav Bryantsev vyachesla... at gmail.com
Wed Apr 24 16:22:27 UTC 2019

```Dear CP2K Group,

There are a couple of ways to setup antiferromagnetic calculations for 6
Cr3+ ions (3d3 state) dissolved in MgCl2-KCl melt.

One way is to use MAGNETIZATION keyword. Another way is to use the BS
section (commented below)

&KIND Cr1
ELEMENT Cr
BASIS_SET DZVP-MOLOPT-SR-GTH
POTENTIAL GTH-PBE-q14
*MAGNETIZATION 4.0*
&DFT_PLUS_U
L 2
U_MINUS_J 0.1234777
# U = 3.36 eV
U_RAMPING 0.01234777
&END DFT_PLUS_U

*!       &BS !        &ALPHA !         NEL +1 -1 !         L 2 0 !
N 3 4 !       &END ALPHA !       &BETA !        NEL -5 -1 !        L 2 0 !
N 3 4 !      &END BETA*
&END BS
&END KIND
&KIND Cr2
ELEMENT Cr
BASIS_SET DZVP-MOLOPT-SR-GTH
POTENTIAL GTH-PBE-q14
*MAGNETIZATION -4.0*
&DFT_PLUS_U
L 2
U_MINUS_J 0.1234777
# U = 3.36 eV
U_RAMPING 0.01234777
&END DFT_PLUS_U

*!       &BS!        &ALPHA!         NEL -5 -1!         L 2 0!         N 3
4!       &END ALPHA!       &BETA!        NEL +1 -1!        L 2 0!        N
3 4!      &END BETA*
&END KIND

The problem I have is that the total E from two setups (MAGNETIZATION and
BS) can be somewhat different:
For example, the Etot of a system (mol fractions are shown) is lower when
setting up calculations using BS
50-MgCl2-50-KCl-5-CrCl3
Etot = -8997.64290729994173 using BS section
Etot = -8997.62650294793639 using MAGNETIZATION keyword

However, for a different composition, the Etot is lower using MAGNETIZATION
15-MgCl2-85-KCl-5-CrCl3
Etot = -6895.30145964661006 using BS section
Etot = -6895.31001188029859 using MAGNETIZATION keyword

The resulting spin moment on each Cr3+ in both cases are close to +3 and
-3, as expected.

*What are the general recommendations to correctly find a ground electronic
state using DFT+U for transition metal ions in solution/melts?*

*Are there any additional checks one can do to make sure the ground
electronic state is found?*
After the ground electronic state is found, the next step will be to run
AIMD simulations.
The input and output files for these examples are given as attachments.

Thank you,
Slava

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```