TY - JOUR
T1 - Quantifying thermal disorder in metal-organic frameworks
T2 - Lattice dynamics and molecular dynamics simulations of hybrid formate perovskites
AU - Svane, Katrine L.
AU - Walsh, Aron
N1 - Publisher Copyright:
© 2016 American Chemical Society.
PY - 2017/1/12
Y1 - 2017/1/12
N2 - Hybrid organic.inorganic materials are mechanically soft, leading to large thermoelastic effects which can affect properties such as electronic structure and ferroelectric ordering. Here we use a combination of ab initio lattice dynamics and molecular dynamics to study the finite temperature behavior of the hydrazinium and guanidinium formate perovskites, [NH2NH3][Zn(CHO2)3] and [C-(NH2)3][Zn(CHO2)3]. Thermal displacement parameters and ellipsoids computed from the phonons and from molecular dynamics trajectories are found to be in good agreement. The hydrazinium compound is ferroelectric at low temperatures, with a calculated spontaneous polarization of 2.6 μC cm-2, but the thermal movement of the cation leads to variations in the instantaneous polarization and eventually breakdown of the ferroelectric order. Contrary to this the guanidinium cation is found to be stationary at all temperatures; however, the movement of the cage atoms leads to variations in the electronic structure and a renormalization in the bandgap from 6.29 eV at 0 K to an average of 5.96 eV at 300 K. We conclude that accounting for temperature is necessary for quantitative modeling of the physical properties of metal-organic frameworks.
AB - Hybrid organic.inorganic materials are mechanically soft, leading to large thermoelastic effects which can affect properties such as electronic structure and ferroelectric ordering. Here we use a combination of ab initio lattice dynamics and molecular dynamics to study the finite temperature behavior of the hydrazinium and guanidinium formate perovskites, [NH2NH3][Zn(CHO2)3] and [C-(NH2)3][Zn(CHO2)3]. Thermal displacement parameters and ellipsoids computed from the phonons and from molecular dynamics trajectories are found to be in good agreement. The hydrazinium compound is ferroelectric at low temperatures, with a calculated spontaneous polarization of 2.6 μC cm-2, but the thermal movement of the cation leads to variations in the instantaneous polarization and eventually breakdown of the ferroelectric order. Contrary to this the guanidinium cation is found to be stationary at all temperatures; however, the movement of the cage atoms leads to variations in the electronic structure and a renormalization in the bandgap from 6.29 eV at 0 K to an average of 5.96 eV at 300 K. We conclude that accounting for temperature is necessary for quantitative modeling of the physical properties of metal-organic frameworks.
UR - http://www.scopus.com/inward/record.url?scp=85019418485&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.6b10714
DO - 10.1021/acs.jpcc.6b10714
M3 - Article
AN - SCOPUS:85019418485
SN - 1932-7447
VL - 121
SP - 421
EP - 429
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 1
ER -