Vector Spherical Harmonic

The spherical harmonics can be generalized to vector spherical harmonics by looking for a scalar function psi and a constant vector c such that

M=del x(cpsi)
=psi(del xc)+(del psi)xc
=(del psi)xc
=-cxdel psi,


 del ·M=0.

Now interchange the order of differentiation and use the fact that multiplicative constants can be moving inside and outside the derivatives to obtain

del ^2M=del ^2(cxpsi)
=del xdel ^2(cpsi)
=del x(cdel ^2psi)


k^2M=k^2del x(cpsi)
=del x(ck^2psi).

Putting these together gives

 del ^2M+k^2M=del x[c(del ^2psi+k^2psi)],

so M satisfies the vector Helmholtz differential equation if psi satisfies the scalar Helmholtz differential equation

 del ^2psi+k^2psi=0.

Construct another vector function

 N=(del xM)/k,

which also satisfies the vector Helmholtz differential equation since

del ^2N=1/kdel ^2(del xM)
=1/kdel x(del ^2M)
=1/kdel x(-k^2M)
=-kdel xM

which gives

 del ^2N+k^2N=0.

We have the additional identity

del xN=1/kdel x(del xM)
=1/kdel (del ·M)-1/kdel ·(del M)
=-1/kdel ·(del M)
=-(del ^2M)/k

In this formalism, psi is called the generating function and c is called the pilot vector. The choice of generating function is determined by the symmetry of the scalar equation, i.e., it is chosen to solve the desired scalar differential equation. If M is taken as

 M=del x(rpsi),

where r is the radius vector, then M is a solution to the vector wave equation in spherical coordinates. If we want vector solutions which are tangential to the radius vector,

M·r=r·(del psixc)
=(del psi)·(cxr)



and we may take


(Arfken 1985, pp. 707-711; Bohren and Huffman 1983, p. 88).

A number of conventions are in use. Hill (1954) defines


Morse and Feshbach (1953) define vector harmonics called B, C, and P using rather complicated expressions.

Explore with Wolfram|Alpha


Arfken, G. "Vector Spherical Harmonics." §12.11 in Mathematical Methods for Physicists, 3rd ed. Orlando, FL: Academic Press, pp. 707-711, 1985.Blatt, J. M. and Weisskopf, V. "Vector Spherical Harmonics." Appendix B, §1 in Theoretical Nuclear Physics. New York: Wiley, pp. 796-799, 1952.Bohren, C. F. and Huffman, D. R. Absorption and Scattering of Light by Small Particles. New York: Wiley, 1983.Hill, E. H. "The Theory of Vector Spherical Harmonics." Amer. J. Phys. 22, 211-214, 1954.Jackson, J. D. Classical Electrodynamics, 2nd ed. New York: Wiley, pp. 744-755, 1975.Morse, P. M. and Feshbach, H. Methods of Theoretical Physics, Part II. New York: McGraw-Hill, pp. 1898-1901, 1953.

Referenced on Wolfram|Alpha

Vector Spherical Harmonic

Cite this as:

Weisstein, Eric W. "Vector Spherical Harmonic." From MathWorld--A Wolfram Web Resource.

Subject classifications