In the Hamilonian for an H(adsbygoogle = window.adsbygoogle || []).push({}); _{2}^{+}, the kinetic energy of the electron (KE of nucleus ignored due to born-oppenheimer approximation) has a negative sign in front of it.

I understand the signs for the potential energy operators but not for the KE apart from the strictly mathematical point of view. Can someone explain this please?

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# I Why is the KE operator negative in QM?

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