Universal attosecond response to the removal of an electron.

When an electron is suddenly removed, a universal response of the system is shown to occur on an attosecond (10(-18) s) time scale. During this response time, which lasts about 50 attoseconds, the density of the created hole changes in a characteristic way. Explicit examples are shown. The results are analyzed in terms of the eigenstates of the residual ion and related to the filling of the exchange-correlation hole associated with the electron in the ground state of the system by the remaining electrons.