A list of orientations for which resonance fields should be computed. It can be either a 2xn or a 3xn array, containing the orientations along columns. Either two (φ, θ) or three (φ, θ, χ) Euler angles (in radians) characterise each orientation.

φ, in the first row, is the angle between the x axis and the xy plan projection of the orientation of the external field in the reference frame of the spin system. θ, in the second row, is the angle at which the external field is off the z axis of the reference frame. The optional χ, in the third row, specifies the third Euler angle and fixes the x axis of the laboratory in the reference frame of the spin system.

Altogether, these three angles define the relative orientation between the molecular reference frame and the laboratory coordinate system. Resonance fields depend only on the first two angles, intensities also on the third.

If the third angle is not given, EPR intensities are integrated over all possible values of χ.

This field specifies populations for the states of the spin system, either directly or via a temperature.

Thermal equilibium:
Temperature is the temperature of the spin system in the EPR experiment, in Kelvin. If given, Boltzmann populations are computed and included in the EPR line intensities. E.g., Temperature = 298 corresponds to room temperature. If not given (or set to inf), all transitions are assumed to be equal polarizations.

Non-equilibrium populations:
Temperature can also be used to specify non-equilibrium populations. For a spin system with N electron states (e.g. 4 for a biradical), it must be a vector with N elements giving the populations of the zero-field electron states, from lowest to highest in energy.
E.g., if Temperature = [0.85 0.95 1.2] for an S=1 system, the population of the lowest-energy zero-field state is 0.85, and the highest-energy zero-field state has a population of 1.2. The populations of all nuclear sublevels within an electron spin manifold are assumed to be equal.

Specifies the symmetry of the crystal. The crystal symmetry can be either the number of the space group (between 1 and 230), the symbol of the space group (e.g. 'P21212' or the symbol for the point group (e.g. 'C2h' or '2/m').

Exp.CrystalSymmetry = 'P21/m'; % space group symbol
Exp.CrystalSymmetry = 11;      % space group number (between 1 and 230)
Exp.CrystalSymmetry = 'C2h';   % point group, Schönflies notation
Exp.CrystalSymmetry = '2/m';   % point group, Hermann-Mauguin notation

When CrystalSymmetry is given, resfields automatically computes the spectra of all symmetry-related sites in the crystal. If CrystalSymmetry is not given, resfields assumes space group 1 (P1, point group C1), which has only one site per unit cell.