Exceptional Configurations with the Clover Action
  We study exceptional modes of both the Wilson and the clover action in order to understand why quenched clover spectroscopy suffers so severely from exceptional configurations. We show that a large clover coefficient can make the exceptional modes extremely localized and thus very sensitive to short distance fluctuations. We contrast this with the case of the Wilson action where exceptional modes correspond to large instantons. These modes are broadly extended and suffer much less from discretization errors. 
Thomas DeGrand, Anna Hasenfratz, Tamas G. Kovacs