# 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:

$Q_\mathrm{rot}^\mathrm{cl}(T) = \frac{\pi^{1/2}}{\sigma} \left( \frac{8 k_\mathrm{B} T}{h^2} \right)^{3/2} \sqrt{I_\mathrm{A} I_\mathrm{B} I_\mathrm{C}}$
as_dict(self) dict

A helper function for dumping objects as dictionaries for YAML files

Returns:

A dictionary representation of the object

Return type:

dict

get_density_of_states(self, ndarray e_list, ndarray dens_states_0=None) ndarray

Return the density of states $$\rho(E) \ dE$$ at the specified energies e_list in J/mol above the ground state. If an initial density of states dens_states_0 is given, the rotor density of states will be convoluted into these states.

get_enthalpy(self, double T) double

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

get_entropy(self, double T) double

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

get_heat_capacity(self, double T) double

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

get_partition_function(self, double T) double

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

get_sum_of_states(self, ndarray e_list, ndarray sum_states_0=None) ndarray

Return the sum of states $$N(E)$$ at the specified energies e_list in J/mol above the ground state. If an initial sum of states sum_states_0 is given, the rotor sum of states will be convoluted into these states.

inertia

The moments of inertia of the rotor.

make_object(self, dict data, dict class_dict)
quantum

‘bool’

Type:

quantum

rotationalConstant

The rotational constant of the rotor.

symmetry

‘int’

Type:

symmetry