No subject

x Phi(i1,i2, na, nb) for pairs of atoms in the super-cell with the relative=
 positions given  by
 R =3D (i-1)*a + (j-1)*b +(k-1)*c
 where i j and k are read from Al444.fc file.
 However, such a supercell does not include the pair of atoms located along=
 the cube axis direction i.e R =3D (a,0,0) or (0,a,0) or (0,0,a), and hence=
 the calculation CAN NOT give us the force-constant matrices along those pa=
ir of atoms.
 How do we obtain the force-constant matrices for pair of atoms located alo=
ng the cube axes direction.
 I will be VERY VERY GRATEFUL to any help in this regard.

Sandeep K. Lahiri
Department of Mechanical Engineering
Massachusetts Institute of Technology
Cambridge, MA=