and as the global softness itself, it is defined in the grand canonical ensemble (open-system representation 42, 47 ), where the chemical potential  is an independent variable for the grand potential: [𝑣(𝐫), ] = 𝐸 -𝑁. 42, Since the variables N and  are related, the hypersoftness 𝑆 may be expressed in both ensembles: 35