Specifies the reference potential in adiabatic switching simulations to compute free energy.  Options are:

<p>
<tt>0</tt>: Einstein crystal (not implemented yet). <br>
<tt>1</tt>: Harmonic potential. <br>
<tt>2</tt>: Inverse-12 (I12) potential. <br>
<tt>3</tt>: Inverse-12 (I12) potential * &lambda;. <br>
<tt>4</tt>: Original potential * &lambda; (i.e. reversible scaling method). <br>
<tt>5</tt>: Gaussian potential. <br>
<tt>6</tt>: Gaussian potential * &lambda;. <br>
<tt>10</tt>: User defined potential. <br>
<tt>20</tt>: Calling VASP to evaluate potential. <br>

<p>
Also see <tt>I12_epsilon</tt>, <tt>Gauss_epsilon</tt>, <tt>runMDSWITCH</tt>, <tt>runMCSWITCH</tt>.

