Past exam of the chemistry course of the year 3 of the natural sciences course of the University of Cambridge / 2022 / Paper 4 / 58 / a / i

Reality of the electron density implies $F(-h)=F(h{)}^{\ast }$. Writing $F(h)=|F(h)|e^{i{\varphi }_h}$ and pairing positive and negative indices givesThe sign in the cosine follows from the supplied negative-sign Fourier-synthesis convention. $F(0)$ is the mean electron density in the fractional-coordinate normalization.