Dear All
In a tetragonal unit cell of MAPbI3 (containing 4 units of MAPbI3), after making a 2*1*1 supercell, I have replaced one MA+ with smaller cation and did relaxation using ISIF =3 in VASP. I was expecting a decrease in the values of average Pb-I bond length and average Pb-I-Pb angle after doping with smaller cation (due to strain relief in the extended PbI6 octahedra) but the increased values of these bond lengths and bond angles was observed, which increased the unit cell volume. What might be the reason for that?
Thanks in advance.
Dear Ankur,
Why are you using ISIF = 3 to relax a tetragonal unit cell
Dear Sinhue,
I am using ISIF= 3 because I wish to relax both lattice constants as well as atomic coordinates of the supercell after doping to get the most stable configuration. In your opinion, why should I not use ISIF=3?
Hi Ankur,
I think this is due to the vibrational modes of cation and/or the rotation of PbI6 octahedra.
Article Fluctuations and Anharmonicity in Lead Iodide Perovskites fr...
Article Density of States Broadening in CH 3 NH 3 PbI 3 Hybrid Perov...
Hope that helps you
Hilal
Dr. Balout!
Thanks for the reply but my calculations were performed at 0K so I have considered a static structure only. The references that you have provided are indeed good but are based on MD calculations. So i don't think that might be the reason here.
Can the reduction in number of H-bonds (between H and I) in structure leads to expansion of cell despite adding a smaller cation?
Hi Ankur,
It was to give you an idea. Cell and atoms optimization at 0K can also lead to little rotation of PbI6 octahedra.
The expansion of cell due to high inter-atomic distances, so reduction in number of H-bonds can be one of this reason.
Hilal.
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