Dipole moment

The electric dipole moment is a measure of polarity. It is the second term in a multipole expansion of a field (the first one being the monopole, or Coulombic, term.) Its definition, for a system of point charges, is given by

$\mathbf {p} =\sum _{i=1}^{N}\,q_{i}\,\mathbf {r} _{i}.$

For molecular systems, it is customarily given in units of Debyes, after the physicist Peter J. W. Debye. In SI units, Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 1} D equals approximately Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 3.33564\times 10^{-30}} Coulomb-meter (exactly Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 10^{-21}} C mFailed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle ^2} /s divided by $c$, the speed of light in vacuum). Conversely, 1 C m = Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 2.9979 10^{29}} D. This is unit is convenient for molecular systems since 1ÅFailed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \times 1 e=4.80320} D.

References

Related reading

• Carlos Vega "Water: one molecule, two surfaces, one mistake" Molecular Physics 113 pp. 1145-1163 (2015)