The reciprocal lattice is a lattice of points in momentum space that is dual to the direct lattice of points in real space.
It is defined as the set of all vectors G that satisfy the equation.
G⋅R=2πn,
where, R is any vector in the direct lattice,
and n is an integer.
In two dimensions, the reciprocal lattice is also a two-dimensional lattice.
For a square lattice with lattice constant a, the direct lattice is defined by the vectors.
The reciprocal lattice vectors are given by;
To find the reciprocal lattice vector corresponding to the (1,1) direction in the direct lattice,
we take a linear combination of the reciprocal lattice vectors.
Thus, the reciprocal lattice vector corresponding to the (1,1) direction in the direct lattice is.