Volume 171, number 3 CHEMICAL PHYSICS LETTERS 3 August 1990 Frequency-dependent hyperpolarizabilities of haloforms from ab initio SCF calculations S.P. Kama and M. Dupuis IBM Corporation, Data System Division, Department 48B/MS 428, Neighborhood Road, Kingston, NY 12401, USA Received 16 April 1990 Ab initio calculations of the frequency-dependent polarizabilities and first and second hyperpolarizabilities of the haloform series have been performed within the framework of the time-dependent coupled perturbed Hartree-Fock method. Dynamic polarizabilities show reasonably good agreement with available experimental data. The theoretical value of/3(SHG) for CHFl is in excellent agreement with the experiment gas phase data. A large discrepancy is noted between theory and experiment for the other molecules both for/I and y. For CHI,, the magnitude of y and its dispersion are large, in accord with experiment. 1. Introduction There is considerable interest in the nonlinear op- tical properties of the haloform series CHXS in gen- eral and those of iodoform, CH13 in particular [ l- 51, This interest has emerged from recent experi- mental observations [ l-3 ] of very large second- and third-order nonlinear optical susceptibilities of CHI, measured in various crystalline forms and in solu- tions. In this respect, CH13 typifies a unique class of highly nonlinear compounds that does not have the characteristics usually associated with high optical nonlinearity, i.e. the presence of delocalized II elec- trons and /or electron donor-acceptor groups in the system. The larger nonlinear optical susceptibilities of CHIJ are attributed to the presence of rather easily polarizable lone pair electrons of the iodine atoms [ 41. Interest in the nonlinear optical properties of chloroform CHCls arises from the fact that the ex- perimental results on this molecule obtained from measurements in different media [ 6- 111 differ sig- nificantly from each other, sometimes by orders of magnitude [ 5,7,8]. Since the macroscopic suscep- tibilities z(n) are related to the microscopic hyper- polarizabilities, B and y, a study of the molecular properties can provide valuable insight about the nonlinear optical responses of haloforms. In this re- gard, nonempirical quantum mechanical studies of the hyperpolarizabilities have the potential to be useful. We have calculated the dynamic polarizabil- ities and hyperpolarizabilities of the haloforms using time-dependent coupled perturbed Hartree-Fock (CPHF) method as recently implemented [ 121 in the HONDO system of ab initio molecular electronic structure programs [ 131. A similar study on the po- larizability dispersion in the haloform series showed very good agreement with experiment and has al- ready been reported in a previous communication [ 5 1. In the present work, in addition to the static po- larizability (Y (0; O), hyperpolarizability /3(0; 0, 0 ), and second hyperpolarizability ~(0; 0, 0, 0), results of the calculations of the following frequency-depen- dent nonlinear optical properties are reported: Dy- namic polarizability LY ( -co; co); hyperpolarizability for (i ) electrooptic Pockels effect (EOPE) /?( - w; 0, w), (ii) second-harmonic generation (SHG) /3( -2~; o, w), and optical rectification (OR) 8(-w; w, - w); second hyperpolarizability for (i) optical Kerr effect (OKE) y( - o; 0,0, w), dc-elec- tric-field-induced second-harmonic generation (dci EFISHG) y( -2~; 0, o, o), third-harmonic gener- ation (THG) y( -3~; o, w, w), intensity-depen- dent refractive index (IDRI) y( -w; o, w, - w) and doelectric-field-induced optical rectification (dc- EFIOR) ~(0; 0, w, - 0). The present paper is or- ganized as follows: in section 2, we describe the the- oretical approach used in this work, including the 0009-2614/90/$ 03.50 0 1990 - Elsevier Science Publishers B.V. ( North-Holland ) 201