Multicomponent transport model fails for single-species phases

[speth]

Problem description

This is a bit of an oddball edge case, but the multicomponent transport model raises exceptions when computing properties for phases that only define a single species. However, computing properties for a phase where multiple species are defined but representing a pure species state works fine.

Steps to reproduce

>>> import cantera as ct
>>> yaml_ref = """
        phases:
        - name: gas
          thermo: ideal-gas
          species:
          - gri30.yaml/species: [H2]
    """
>>> gas = ct.Solution(yaml=yaml_ref)
>>> gas.transport_model = 'multicomponent'
>>> print(gas.thermal_conductivity)
CanteraError: 
*******************************************************************************
CanteraError thrown by solve(DenseMatrix& A, double* b):
DGETRF returned INFO = 1. U(i,i) is exactly zero. The factorization has been completed, but the factor U is exactly singular, and division by zero will occur if it is used to solve a system of equations.
*******************************************************************************

>>> print(gas.multi_diff_coeffs)
CanteraError: 
*******************************************************************************
CanteraError thrown by invert(DenseMatrix& A, size_t nn):
DGETRS returned INFO = 1
*******************************************************************************

>>> print(gas.thermal_diff_coeffs)
CanteraError: 
*******************************************************************************
CanteraError thrown by solve(DenseMatrix& A, double* b):
DGETRF returned INFO = 1. U(i,i) is exactly zero. The factorization has been completed, but the factor U is exactly singular, and division by zero will occur if it is used to solve a system of equations.
*******************************************************************************

Expected Behavior

I think the computed thermal conductivity should be the pure species thermal conductivity, the multicomponent diffusion coefficients should be a 1x1 matrix of [[0.0]] and the thermal diffusion coefficient should be a 1-element array [0.0].

System information

• Cantera version: 3.1.0b1
• OS: macOS Sequoia 15.1
• Python/MATLAB/other software versions: Python 3.11, Apple Clang 16.0.0