# rmgpy.statmech.NonlinearRotor¶

class rmgpy.statmech.NonlinearRotor(inertia=None, symmetry=1, quantum=False, rotationalConstant=None)

A statistical mechanical model of an N-dimensional nonlinear rigid rotor. The attributes are:

Attribute Description
inertia The moments of inertia of the rotor
rotationalConstant The rotational constants of the rotor
symmetry The symmetry number of the rotor
quantum True to use the quantum mechanical model, False to use the classical model

Note that the moments of inertia and the rotational constants are simply two ways of representing the same quantity; only one set of these can be specified independently.

In the majority of chemical applications, the energies involved in the rigid rotor place it very nearly in the classical limit at all relevant temperatures; therefore, the classical model is used by default. In the current implementation, the quantum mechanical model has not been implemented, and a NotImplementedError will be raised if you try to use it.

A nonlinear rigid rotor is the generalization of the linear rotor to a nonlinear polyatomic system. Such a system is characterized by three moments of inertia $$I_\mathrm{A}$$, $$I_\mathrm{B}$$, and $$I_\mathrm{C}$$ instead of just one. The solution to the Schrodinger equation for the quantum nonlinear rotor is not well defined, so we will simply show the classical result instead:

$Q_\mathrm{rot}^\mathrm{cl}(T) = \frac{\pi^{1/2}}{\sigma} \left( \frac{8 k_\mathrm{B} T}{h^2} \right)^{3/2} \sqrt{I_\mathrm{A} I_\mathrm{B} I_\mathrm{C}}$
getDensityOfStates(self, ndarray Elist, ndarray densStates0=None) → ndarray

Return the density of states $$\rho(E) \ dE$$ at the specified energies Elist in J/mol above the ground state. If an initial density of states densStates0 is given, the rotor density of states will be convoluted into these states.

getEnthalpy(self, double T) → double

Return the enthalpy in J/mol for the degree of freedom at the specified temperature T in K.

getEntropy(self, double T) → double

Return the entropy in J/mol*K for the degree of freedom at the specified temperature T in K.

getHeatCapacity(self, double T) → double

Return the heat capacity in J/mol*K for the degree of freedom at the specified temperature T in K.

getPartitionFunction(self, double T) → double

Return the value of the partition function $$Q(T)$$ at the specified temperature T in K.

getSumOfStates(self, ndarray Elist, ndarray sumStates0=None) → ndarray

Return the sum of states $$N(E)$$ at the specified energies Elist in J/mol above the ground state. If an initial sum of states sumStates0 is given, the rotor sum of states will be convoluted into these states.

inertia

The moments of inertia of the rotor.

quantum

quantum – ‘bool’

rotationalConstant

The rotational constant of the rotor.

symmetry

symmetry – ‘int’