I'm new in fpga. but it's really interesting for me.
do they really work? I mean can we write a program in vhdl or Verilog language and convert it to a spice model and simulate it in an analog and digital mixed simulator such as orcad or altium?
I've never used spice models for FPGAs, but I believe they just model the I/O, not the internal logic, i.e., your VHDL/Verilog. You can simulate the logic using any number of simulators that will do either functional or timing simulation. Functional simulation just simulates your code without consideration of the physical device; timing simulation actually models the performance of the silicon.
Actually, you CAN specify simulations for different voltages or temperatures. Manufacturers provide minimum, maximum and typical simulation models for temp and voltage. But, you are right, they are not spice models.