How to model a Schottky diode based on datasheet?
The spice model is in the datasheet:



It's a little confusing because they tell you to use these parameters:



R1 and LS, Csh are values for the circuit model, the rest are for the diode model.

You make a diode model like this:  


  General form:  d[name] [anode] [cathode] [modelname]
                 .model ([modelname] d [parmtr1=x] [parmtr2=y] . . .)    
  
  Example:       d1 1 2 mod1
                 .model mod1 d    
  
  Example2:      D2 1 2 Da1N4004    
  
  .model Da1N4004 D (IS=18.8n RS=0 BV=400 IBV=5.00u CJO=30 M=0.333 N=2)   


Source: Diode Spice Models - All about circuits.

Draw the circuit up and plug in the other parameters for the diode model.

Here is another way to model a schottky diode if the above model does not sufficiently model all of the dynamics, you would need to take measurements of a real device and fit them to the model:

  

Source: A novel physical parameter extraction approach for Schottky diodes

Edit: 
ADS does use spice models and the model format looks the same. You can also import models from spice into ADS.