I'm told that the MnO crystal resembles in structure that of NaCl (FCC) with lattice constant a, and am first asked to write a general expression for the position vector Rj of the ion j in the unit cell of MnO. I am then asked to find the vector K for MnO in order to use the relation μj=μ0e(iK⋅Rj) to determine the magnetic moment of an ion at the position Rj. I initially wrote down the unit cell vectors for one of the two atoms, and added to these a basis (due to the second atom): a1=a/2(x^+y^),a2=a/2(x^+z^),a3=a/2(y^+z^), with basis: d1=0,d2=a/2(x^+y^+z^). How am I to formulate the expression for the general position vector Rj? Would it simply be a linear combination of all these vectors? Next, for determining the value of the vector K, need I to first find the reciprocal lattice? I'd appreciate some explicit assistance/guidance.