The linear magneto-optical effect, known as the Faraday effect, consists of the rotation of the plane of polarization of linearly polarized light when it propagates through a medium placed in a magnetic field with nonzero component in the direction of light propagation. [1][2][3][4] Far from absorption, the Faraday effect is related to the Verdet constant, [5] a quantity characteristic of the substance which depends on concentration, temperature, and frequency. Using the response formalism, [6] it is represented as Equation (1):where ( m a ; m b ; iL g ) w;0 is the quadratic response function, m and L are the dipole-moment and angular-momentum operators, respectively, and e(a,b,g=x,y,z) is the Levi-Civita tensor. The Einstein summation convention over repeated indices is assumed in Equation (1); w is the circular frequency of the incident light, and C a constant [Eq. (2)]:where N is the number density and the other quantities have their usual meaning. So far, the Verdet constant has been measured for a collection of molecules, [1,7,8] and this has initiated several theoretical investigations. [9][10][11][12][13][14][15][16] In addition to linear response calculations assuming the Becquerel approximation, [9,10] V(w) is evaluated using 1) a sum-over-state expression, [11] 2) quadratic response functions, [12][13][14][15] and, more recently, 3) time-dependent density functional theory (TDDFT). [16] Gauge-independent atomic orbital (GIAO) approaches have been elaborated at both coupled cluster (CC) [14] and TDDFT [16] levels of approximation.Coriani et al. [15] employed a hierarchy of CC response theory models to assess the importance of electron correlation. They evidenced the necessity of including triple excitations for providing a correct estimate of V(w) of the nitrogen and acetylene molecules and pointed out that zero-point vibrational averaging could account for the difference between theory and experiment in the case of methane. Moreover, Krykunov et al. [16] concluded that, when a sufficiently large basis set is used, the TDDFT schemes with nonhybrid exchange-correlation functionals has a clear tendency to slightly overestimate the Verdet constant.On the other hand, little is known about structure-property relationships for organic molecules, which might be of importance in addressing molecular properties [17,18] or designing materials with outstanding magneto-optical properties. As a first step towards this goal, we have measured the dispersion of the Faraday effect for benzene, toluene, and p-xylene as pure liquids and performed theoretical calculations at the DFT level of approximation.Geometry optimizations are carried out for the three compounds at the MP2/6-31G* level of approximation. The V(w) values are evaluated by adopting the analytical quadratic response approach within the density functional theory [19] implemented in the Dalton 2.0 electronic structure program, [20] which retains the adiabatic approximation. Although this scheme allows the use of different exchange-correlation functionals for ...