This is a criterion used in @R05391@ for locating the @T06468@. The @R05168@ \(r\) at the @T06468@, according to this criterion, is given by \(\frac{\partial (N\left(\varepsilon_{\text{r}}\right))}{\partial r}=0\), where \(N\left(\varepsilon_{\text{r}}\right)\) is the density of states at an @I03103@ \(\varepsilon_{\text{r}}\).