Comparison of the X-ray atomic form factors for crystalline and free-atom lithium

X-ray atomic form factors, f, have been calculated for crystalline and free-atom lithium using the same Gaussian-orbital basis and the same exchange-correlation potential in the local density approximation by the self-consistent linear combination of Gaussian orbitals (LCGO) method. The difference between f calculated for an Li crystal and f for free Li atoms is less than 0.8%, which is rather small. For free Li atoms the values of f deviate from those obtained by Hartree-Fock calculations by 1.5 to 3% for sin θ/λ < 1.2 Å^-1.