Is this for an assignment or for research? This is something that Verilog-A is built for, SPICE would not be a great choice as it fulfills a different purpose, but you can definitely do it as long as you understand its limitations and properly understand the outputs.
Either way, I don't personally have an understanding of PMUTs, I'm not familiar with MEMS physics, so I'm useless for you there, but this seems like something you need to dig into research papers about.
You need to understand what the purpose of your simulation/modeling is. For example if you're only interested in the signal coming out and how to design a filter for it, you can use Python/Matlab to generate a PWL file and feed that into LTSpice. If, on the other hand, you're designing a circuit that's driving the MEMS and you need to know things like parasitic capacitance, back emf etc. that's a different process.