Claiming that the model is the first model of its kind
In 1988, in their paper Quantum Hall effect devices as circuit elements, Ricketts and Kemeny presented a first circuit model for quantum Hall effect devices [1]. 

Here is how the model is presented in the abstract:


  The electrical behaviour of a quantum Hall effect device is described
  in terms of an equivalent circuit. This circuit is able to model the
  principal electrical characteristics of an ungated Hall bridge device.


In the Introduction:


  In this paper we describe the behaviour of a QHE
  device in terms of an equivalent circuit. 


And in the Conclusions:


  An equivalent circuit has been presented that can represent the DC
  electrical behaviour of a Hall bridge device under QHE conditions.


This is just a random example, but I think that it aptly shows the right way to present a first model: review what is known about that device and its behaviour, so that it becomes evident that, to your knowledge, there isn't any model of that kind currently available; tell the reader what kind of model you are going to describe and what phenomena it can model. 

Then, let the reader decide if it's really a first one.

[1] B. W. Ricketts and P. C. Kemeny, J. Phys. D: Appl. Phys., 21, 483, 1988.