Von Neumann Entropy: varying definitions

I have seen different authors define von Neumann entropy in different ways. In particular, some use the natural logarithm and others log to base 2. What is the reasoning for this? Does it make any difference? What is the accepted definition?

Thank you in anticipation of your help.

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Use that different logarithms are proportional $\log_b \rho =\frac{\ln \rho}{\ln b}$. –  Qmechanic Mar 31 '13 at 10:47