Calculating spin configurations for chains

[Danny]

Hi,

I am currently working on two projects in which I am faceing linear chain systems of which we would like to set the spin configurations and compare the properties of the system as function of the configuration.

The basic setup is as follows for the larger problem:
A bulk system contains 2 paralell chains (2 atoms per chain in our cell) and we wish to compare the paramagnetic setup with two anti-ferromagnetic setups (A: antiferromagnetic behavior in each chain: ie: +- and -+ along a chain, B anti-ferromagnetism between the chains: ++ and --)

for this I used the following INCAR settings:
NUPDOWN = 0 (=4 for the paramagnetic)
MAGMOM = +2.0 +2.0 -2.0 -2.0 68*0.0 (for the antiferromagnetic B configuration)

I switch " LORBIT = 11 " to get magnetic data and for the calculations.

I also keep WAVECAR and CHGCAR files to use for continuations of the ralaxations.

The problems that I encounter are multiple (and probably related):
When starting a relaxation with the above settings, I often get a magnetization of exactly zero

Code: Select all

?magnetization?(x)

#?of?ion?????s???????p???????d???????tot
----------------------------------------
??1????????0.000???0.000???0.000???0.000
??2????????0.000???0.000???0.000???0.000
??3????????0.000???0.000???0.000???0.000
??4????????0.000???0.000???0.000???0.000

this can also happen when I continue a successfull relaxation (i.e. magnetizations were about 0.83 for tot and then are zero from the first step of the second relaxation calculation)

In another case, I even ended op with the wrong configuration: for a ++, -- configuration:

MAGMOM = +2.0 +2.0 -2.0 -2.0 68*0.0
I get this:
(grep -A7 "magnetization (x) OUTCAR")

Code: Select all

?magnetization?(x)

#?of?ion?????s???????p???????d???????tot
----------------------------------------
??1????????0.001???0.001???0.178???0.180
??2????????0.004???0.004???0.665???0.673
??3???????-0.004??-0.004??-0.665??-0.673
??4???????-0.001??-0.001??-0.178??-0.180
--
?magnetization?(x)

#?of?ion?????s???????p???????d???????tot
----------------------------------------
??1???????-0.005??-0.006??-0.737??-0.748
??2????????0.005???0.006???0.748???0.759
??3???????-0.005??-0.006??-0.748??-0.759
??4????????0.005???0.006???0.737???0.748
--
?magnetization?(x)

#?of?ion?????s???????p???????d???????tot
----------------------------------------
??1???????-0.006??-0.006??-0.802??-0.813
??2????????0.006???0.006???0.804???0.815
??3???????-0.006??-0.006??-0.804??-0.815
??4????????0.006???0.006???0.802???0.813
--
?magnetization?(x)

#?of?ion?????s???????p???????d???????tot
----------------------------------------
??1???????-0.006??-0.006??-0.807??-0.819
??2????????0.006???0.006???0.809???0.820
??3???????-0.006??-0.006??-0.809??-0.820
??4????????0.006???0.006???0.807???0.819
--
?magnetization?(x)

#?of?ion?????s???????p???????d???????tot
----------------------------------------
??1???????-0.006??-0.006??-0.810??-0.822
??2????????0.006???0.006???0.811???0.823
??3???????-0.006??-0.006??-0.811??-0.823
??4????????0.006???0.006???0.810???0.822
--
?magnetization?(x)

#?of?ion?????s???????p???????d???????tot
----------------------------------------
??1???????-0.006??-0.006??-0.811??-0.823
??2????????0.006???0.006???0.812???0.824
??3???????-0.006??-0.006??-0.812??-0.824
??4????????0.006???0.006???0.811???0.823

Since the chains consist of d-block metals I also set MAXMIX = 4 (to improve the quality of the CHGCAR files) All calculations are at Accurate precision, using IBRION=2 for relaxation.


Does anyone have any suggestions to fix this problem?

kind regards
Danny
PS: chain atoms have 1 unpaired electron, and setting MAGMOM to 2 has improved the situation somewhat.

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