9.4.1 
cell_leakage_power Simple Attribute
This attribute specifies the leakage power of a cell.
If this attribute is missing or negative,the value of the default_cell_leakage_power attribute is used.
Syntax
  cell_leakage_power:value
    float;value
      A floating-point number indicating the leakage power of the cell.
Note:
You must define this attribute for cells with state-dependent leakage power to provide the leakage power value for those states where the state-specific leakage power has not been specified using the leakage_power (leakage_power () {...} ) group.
<https://people.eecs.berkeley.edu/~alanmi/publications/other/liberty13_03.pdf>