# Regulating the sum in Casimir Force

I am trying to evaluate the Casimir force using a Gaussian regulator (I know there are other much easier ways to do this, but I want to try this!) We then are reduced to evaluating the sum

$$\sum\limits_{n=1}^\infty n e^{-\alpha n^2}$$

Moreover, I am interested in the series expansion of the above sum around $\alpha = 0$. Any ideas how I would go about obtaining this sum?

PS - I don't want to use the Euler-Mclaurin formula.That was used to show that a general regulator would always give one the same answer, so this would just be a special case of the that proof and not a very novel way. Any other ideas?

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–  Qmechanic Nov 21 '12 at 19:21