Multiconfigurational linear response

However, until today no systematic comparison of methods based on MpUer-Plesset perturbation (MP) and Coupled Cluster theory, the SOPPA or multiconfigurational linear response theory has been presented. The present study is a first attempt to remedy this situation. Calculations of the rotational g factor of HF, H2O, NH3 and CH4 were carried out at the level of Hartree-Fock (SCF) and multiconfigurational Hartree-Fock (MCSCF) linear response theory, the SOPPA and SOPPA(CCSD) [40], MpUer-Plesset perturbation theory to second (MP2), third (MP3) and fourth order without the triples contributions (MP4SDQ) and finally coupled cluster singles and doubles theory. The same basis sets and geometries were employed in all calculations for a given molecule. The results obtained with the different methods are therefore for the first time direct comparable and consistent conclusions about the performance of the different methods can be made. 

Spin-Orbit Coupling Constants in a Multiconfiguration Linear Response Approach. 

Olsen J, Sanchez de Meras, Jensen HJAa, Jprgensen P (1989) Excitation energies, transition moments and dynamic polarizabilities for CH+ A comparison of multiconfigurational linear response and full configuration calculations. Chem Phys Lett 154 380-386. 

There are, however, many pieces of evidence that the cysteine link only causes small perturbations in the electronic structure and energetics of tyrosine. Electrochemical experiments by Whittaker et al [31] showed that the p fiTa of o-methylthiocresol was only 0.7 pH units lower than for cresol (9.5 vs. 10.2). Babcock and co-workers have shown, based on EPR and ENDOR experiments on both apo-enzyme and model alkylthio-substituted phenoxyl radicals, that the sulfur cross-link only induces small perturbation in the spin distribution of the tyrosyl radical [32]. No big shift in the g-tensors between unsubstituted and methylthio-substituted radicals was observed. Since this kind of shift is expected when heavy elements carry some of the spin in organic radicals, the conclusion was that the sulfur center possesses only a small part of the unpaired spin. We have conducted ab initio multiconfigurational linear response g-value calculations of unsubstituted and sulfur-substituted phenoxyl radicals and shown that the shift in g-tensor is as small as 0.0008 in the gxx-component (2.0087 vs. 2.0079 in t). The other components were virtually unchanged, thus confirming the experimental results [33]. 

R.L. Graham, D.L. Yeager, J. Olsen, P. Jorgensen, R. Harrison, S. Zarrabian, R. Bartlett, Excitation energies in Be A comparison of multiconfigurational linear response and full configuration interaction calculations, J. Chem. Phys. 85 (1986) 6544. 

R. Berger, M. Quack, Multiconfiguration linear response approach to the calculation of parity violating potentials in polyatomic molecules, J. Chem. Phys. 112 (2000) 3148-3158. 

Ab initio determinations of SOC in carbene (1) have been carried out for three bond angles (0 = 90, 112 and 135°) by McKellar et al. [27J using SCI and SDCI wave functions and by Vahtras et al. [19] for the equilibrium geometry employing a multiconfiguration linear response (MCLR) approach. Both sets of calculations are based on the full coupling operator with the... 

J. Olsen, D. Yeager, P. Jprgensen, Triplet excitation properties in large scale multiconfiguration linear response calculations, J. Chem. Phys. 91 (1989) 381-388. 

AIMD = ab initio molecular dynamics B-LYP = Becke-Lee-Yang-Parr CCSD = coupled cluster single double excitations CVC = core-valence correlation ECP = effective core potential DF = density functional GDA = gradient corrected density approximation MCLR = multiconfigurational linear response MP2 = M0ller-Plesset second-order (MRD)CI = multi-reference double-excitation configuration interaction RPA = random phase approximation TD-MCSCF = time-dependent multiconfigurational self-consistent field TD-SCF = time-dependent self-consistent field. 

The linear response methods offer a viable alternative to the Cl procedure [38]. A time-dependent (TD) perturbation theory (e.g. involving an oscillating electric field), combined with the SCF or MCSCF method is referred to as the TD-SCF (or random phase approximation, RPA) or the TD-MCSCF (or multiconfigurational linear response, MCLR), respectively. Let us consider the time development of the dipole moment (z-component for simplicity) ... 

M. Jaszunski, A. Rizzo, and D. L. Yeager, Chem. Phys., to be published. A Multiconfigurational Linear Response Study of Na. 

Vahtras, O., Agren, H., Jprgensen, P., Jensen, H. J. Aa., Padkjaer, S. B., and Helgaker, T. (1992). Indirect nuclear spin-spin coupling constant from multiconfigurational linear response theory. J. Chem. Phys., 96, 6120A5125. 

The use of multiconfiguration linear response (MCLR) theory is another approach to the calculation of spin-spin coupling interactions. As is usual for ab initio MO calculations, the results obtained are found to be basis set dependent. In general, satisfactory agreement with the available experimental data is achieved. 

Agren H, Cairavetta V, Jensen HJA, Jprgensen P, Olsen J. Multiconfiguration linear-response approaches to the calculation of absolute photoionization cross sections HF, H2O, and Ne. 

---