I am try to optimize molecule at 0 K using keyword "Temperature=0" but gaussian performs calculation at 298 K. How to get my required thermodynamic parameter at 0K
In Gaussian, Temperature= … imposes the temperature of thermochemical calculations (https://gaussian.com/temp/). By definition ZPE is not dependent on the temperature. What changes by increasing T is not ZPE, but the population of higher vibrational states of the GS. See K. K. Irikura "Experimental Vibrational Zero-Point Energies: Diatomic Molecules" J. Phys. Chem. Ref. Data 36(2), 389, 2007.