HSPICE or Spetre are not open source tools. They are owned by Synopsys and Cadence respectively. You can use some university tools like IRSIM as pointed out by Dr.CP Ravikumar.
any SPICE supporting simulators shall take switch level modeling of CMOS circuit design and produce both DC and transient response. XILINX mainly focuses on FPGA design for which neither switch level modelling nor CMOS circuit topology is needed.