I calculated the dispersion relation of the R3m phase of BaTiO3, and it seems incorrect, with spurious imaginary frequencies appearing

[liudadie12138]

Hello
I am trying to calculate the dispersion relations of the four phases of BaTiO3. When calculating the R3m phase, it seems to have a problem. Specifically: it should be stable at low temperatures, but there are unexpected imaginary frequencies. I used a 2×2×2 supercell and then tried a 3×3×3, but it didn't change. So I continued to calculate scph, and the results show that although it converges at temperature, there are still imaginary frequencies. Additionally, when calculating the pm3m phase, I encountered the same problem. Although the calculation results show convergence, there are still imaginary frequencies. How should these two problems be solved. This is the specific alm.in
&general
PREFIX = BTO222
MODE = suggest
NAT = 40
NKD = 3
KD = Ba Ti O
/

&interaction
NORDER = 1
/

&cell
1.889726
8.0075883595 -0.0135854367 -0.0135065974
0.0332919341 8.0075306772 -0.0135065969
0.0332919336 0.0330976063 8.0074736667
/

&cutoff
Ba-Ba None
Ba-Ti None
Ba-O None
Ti-Ti None
Ti-O None
O-O None
/

&position
1 0.999091132 0.999091132 0.999091132
1 0.999091132 0.999091132 0.499091132
1 0.999091132 0.499091132 0.999091132
1 0.999091132 0.499091132 0.499091132
1 0.499091132 0.999091132 0.999091132
1 0.499091132 0.999091132 0.499091132
1 0.499091132 0.499091132 0.999091132
1 0.499091132 0.499091132 0.499091132
2 0.255109706 0.255109706 0.255109706
2 0.255109706 0.255109706 0.755109706
2 0.255109706 0.755109706 0.255109706
2 0.255109706 0.755109706 0.755109706
2 0.755109706 0.255109706 0.255109706
2 0.755109706 0.255109706 0.755109706
2 0.755109706 0.755109706 0.255109706
2 0.755109706 0.755109706 0.755109706
3 0.243387142 0.243387142 0.489774878
3 0.243387142 0.243387142 0.989774878
3 0.243387142 0.743387142 0.489774878
3 0.243387142 0.743387142 0.989774878
3 0.743387142 0.243387142 0.489774878
3 0.743387142 0.243387142 0.989774878
3 0.743387142 0.743387142 0.489774878
3 0.743387142 0.743387142 0.989774878
3 0.243387142 0.489774878 0.243387142
3 0.243387142 0.489774878 0.743387142
3 0.243387142 0.989774878 0.243387142
3 0.243387142 0.989774878 0.743387142
3 0.743387142 0.489774878 0.243387142
3 0.743387142 0.489774878 0.743387142
3 0.743387142 0.989774878 0.243387142
3 0.743387142 0.989774878 0.743387142
3 0.489774878 0.243387142 0.243387142
3 0.489774878 0.243387142 0.743387142
3 0.489774878 0.743387142 0.243387142
3 0.489774878 0.743387142 0.743387142
3 0.989774878 0.243387142 0.243387142
3 0.989774878 0.243387142 0.743387142
3 0.989774878 0.743387142 0.243387142
3 0.989774878 0.743387142 0.743387142
/