  We use molecular dynamics with a first-principles based shell model potential
to study pyroelec- tricity in lithium niobate. We find that the primary
pyroelectric effect is dominant, and pyroelec- tricity can be understood simply
from the anharmonic change in crystal structure with temperature and the Born
effective charges on the ions. This opens a new experimental route to studying
py- roelectricity, as candidate pyroelectric materials can be studied with
X-ray diffraction as a function of temperature in conjunction with theoretical
effective charges. We also predict an appreciable pressure effect on
pyroelectricity, which could be used to optimize materials pyroelectricity, and
the converse electrocaloric effect, peak as Tc is approached.
