a = 5.65*10^-8; //lattice constant in cm
disp("In the (001) surfaces, the top atoms are either Ga or As leading to the terminology Ga terminated (or Ga stabilized) and As terminated (or As stabilized), respectively. A square of area a2 has four atoms on the edges of the square and one atom at the center of the square. The atoms on the square edges are shared by a total of four squares. The total number of atoms per square is")
N = 4/4 +1; 
disp(N)
density = N/a^2; //Surface density
disp(density, "The surface density (in per cm square) of Ga atoms on a Ga terminated (001) GaAs surface")