J. Phys. Chem. 1992, 96, 2069-2079
2069
Weakly Bound Complexes of Carbon Monoxlde Carol A. Parish,+Joseph D.Augspurger, and Clifford E. Dykstra* Department of Chemistry, Indiana University-Purdue University at Indianapolis, I I25 East 38th Street, Indianapolis, Indiana 46205 (Received: September 13, 1991; In Final Form: October 24, 1991)
We have carried out a wide-ranging theoretical investigation of weakly bound complexes containing carbon monoxide that reveals at least one general feature of CO weak bonding, its electrical polarization. Included in this study are high-level ab initio calculations of two dimer complexes and of the electrical response properties of CO. The electrical properties were used in model calculations of weakly bound complexes of CO and, in particular, to achieve a representation of CO for the electrical interaction scheme of the molecular mechanics for clusters (MMC) model. MMC calculations were carried out to explore the difference between oxygen-end and carbon-end bonding, and in the course of these calculations predictions of multiple minima have come about for several complexes. The calculational results also provide information about how the properties of CO change upon weak bonding and how electrical polarization influences structure.
Introduction The ability of carbon monoxide to weakly bind to numerous molecular species has important consequences in transition metal complexes, respiratory proteins, and certain biomolecular processes. The fundamental nature of its weak bonding is surely one goal of the efforts to study the spectra of small molecule, weakly bound complexes involving at least one CO constituent.’+ A general model of weak, nonbonding interaction has been incorporated into a computational method called molecular mechanics for clusters (MMC).I6 In this report, we draw on that approach as well as on ab initio electronic structure calculations to understand more of the nature of the weak binding of carbon monoxide. MMC is based on the electrical interaction of atoms and molecules and it involves an extensive treatment of the mutual polarization response of atomic and molecular assemblies. The electrical interaction is evaluated from the intrinsic electrical properties (multipole moments, polarizabilities, and hyperpolarizabilities) of the interacting species, and so far, these have been obtained largely from high level ab initio calculations on isolated molecules. To treat CO complexes with MMC, the first task is to obtain a suitable electrical property set, and that is orie aspect of this work. Nonelectrical interaction effects are treated collectively via pairwise terms in MMC. These are empirical, involving just a small number of parameters. These pairwise terms are meant to represent exchange interaction, dispersion, and other lingering effects possibly including truncation error in the electrical energies. In studying CO complexes, we have included an examination of the relation between the truncation level of the electrical analysis and the parameter selection. Well-correlated, extended basis set a b initio calculations were carried out on the OC-HF complex as a further comparison of the model results. Along with prior a b initio studies,I7J8these results show a basis set sensitivity that is entirely in line with our view of the importance of electrical polarization in CO weak binding. MMC calculations were then carried out on a number of small complexes to test the capability for prediction of structural parameters and then to find secondary minima and interconversion barriers. Electrical Properties of Carbon Monoxide To understand the electrical interaction of C O with other molecules, a number of electrical properties, not all readily available from experiment, need to be obtained from ab initio calculation. Assessment of the reliability of such calculated properties is quite important for using the properties in model calculations, and that calls for a detailed examination of the basis set and correlation effects. This must be done by following the variation of the effects with bond length; using one bond length, such as the equilibrium, may give an incomplete picture, as shown American Chemical Society Petroleum Research Fund Fellow.
in the very case of carbon monoxideI9 and the correlation effect on the dipole.20 CO has been the subject of high level investigations of properties already, and the calculations of Diercksen and Sadlej and co-workers21,22have been particularly extensive with correlation effects treated with configuration interaction, fourth-order MBPT and coupled cluster methods. A first concern in basis set quality involves polarization functions, and there are two aspects, the diffuseness and the I-order of the atomic functions. It is well established [see, for instance, refs 23 and 241 that diffuse polarization functions are important for small covalent molecules, and it is possible that high I-functions (e.g., 4f) could be. A second concern is the effect of electron correlation. Some calculational studies have pointed to effects of 50% in small molecule dipole hyperpolarizabilitie~,~~ though for acetylene, which is isoelectronic to CO, the detailed study of (1) Legon, A. C.; Soper, P. D.; Flygare, W. H. J. Chem. Phys. 1981, 74, 494. (2) (A) Read, W. G.; Campbell, E . J. J. Chem. Phys. 1983,78,6515. (b) Campbell, E. J.; Read, W. G.; Shea, J. A. Chem. Phys. Lett. 1983,94,69. (3) (a) Kyro, E.K.; Shoja-Chaghervand, P.; McMillan, K.; Eliades, M.; Danzeiser, D.; Bevan, J. W. J. Chem. Phys. 1983, 79, 78. (b) Wang, Z.; Bevan, J. W. J. Chem. Phys. 1989, 91, 3335. (4) Goodwin, E. J.; Legon, A. C. Chem. Phys. 1984,87, 81. ( 5 ) Fraser, G.T.; Nelson, D. D., Jr.; Peterson, K. I.; Klemperer, W. J. Chem. Phys. 1986, 84, 2472. (6) Fraser, G.T.; Pine, A. S.J. Chem. Phys. 1988,88, 4147. (7) Jucks, K. W.; Miller, R. E. J. Chem. Phys. 1987,86,6637; 1988,89, 1262. (8) Legon, A. C.; Suckley, A. P. J. Chem. Phys. 1989, 91,4440. (9) Marshall, M. D.; %chard, D. G.; Muenter, J. S. J. Chem. Phys. 1989, 90, 6049. Marshall, M. D.; Kim, J.; Hu, T. A.; Sun, L. H.; Muenter, J. S. J. Chem. Phys. 1991, 94,6334. (IO) Randall, R. W.; Summersgill, J. P. L.; Howard, B. J. J. Chem. Soc., Faraday Trans. 1990, 86, 1943. (11) Ruoff, R. S.;Emilsson, T.; Chuang, C.; Klots, T. D.; Gutowsky, H. S.J. Chem. Phys. 1990, 93, 6363. (12) Emilsson, T.; Klots, T. D.; Ruoff, R. S.; Gutowsky, H. S. J. Chem. Phvs. ,--1990. 93. 6971. - 7
- 7
(13) Legon, A. C.; Wallwork, A. L.; Bevan, J. W.; Wang, Z . Chem. Phys.
Left. 1991, 180, 57. (14) Yaron. D.: Peterson. K.I.: Zolandz. D.: Klemwrer. . W.: Lovas. F. J.: Suenram, R. D. J. Chem. Phys. 1990, 92, 7095. (15) Bumgarner, R. E.; Suzuki, S.;Stockman, P. A,; Green, P. G.; Blake, G. A. Chem. Phys. Lett. 1991, 176, 123. (16) Dykstra, C. E. J. Am. Chem. SOC.1989, 1 1 1 , 6168. (17) Benzel, M. A.; Dykstra, C. E. J. Chem. Phys. 1982, 77, 1602; 1983, 78, 4052. (18) Benzel, M. A.; Dykstra, C. E . Chem. Phys. 1983.80, 273. (19) Raghavachari, K.; Pople, J. A. Inf. J . Quanfum Chem. 1981, 20, 1067. (20) Green, S. J. Chem. Phys. 1971, 54, 827. (21) Diercksen, G. H. F.; Sadlej, A. J. Chem. Phys. 1985, 96, 17, 43. (22) Kello, V.; Noga, J.; Diercksen, G. H. F.; Sadlej, A. J. Chem. Phys. Left. 1988, 152, 387. (23) Werner, H.-J.; Meyer, W. Mol. Phys. 1976, 31, 8 5 5 . (24) Liu, S.-Y.; Dykstra, C. E. J. Phys. Chem. 1987, 91, 1749. (25) Purvis, G. D.; Bartlett, R. J. Phys. Rev. A: Gen. Phys. 1981, 23, 1594.
0022-3654/92/2096-2069$03.00/0 0 1992 American Chemical Society
2070 The Journal of Physical Chemistry, Vol. 96,No. 5, 1992 TABLE I: Calculated Equilibrium and Vibrational State (n = 0, Electrical Properties“of Carbon Monoxide (in au) property equilibrium n =0 n=1 n-2 MZ Mzz MYY P.2 PYY p,,, PZYY Pvvz PZZJZ PYYP PYZYZ PYYYY PXXYV P,,Z PYYJ
0.027 -4.552 -3.834 -14.423 -11.238 -6.277 -0.575 -4.567 -27.101 -0.684 -11.645 -9.047 -2.482 -31.172 -4.767
0.018 -4.550 -3.840 -15.002 -11.278 -6.291 -0.275 -4.557 -27.241 -0.676 -11.720 -9.286 -3.290 -13.623 -2.917
0.007 -4.548 -3.847 -15.194 -11.329 -6.300 -0.272 -4.544 -27.421 -0.676 -11.816 -9.333 -3.301 -14.357 -2.727
1,2)
-0.005 -4.546 -3.853 -15.389 -11.382 -6.310 -0.269 -4.532 -27.605 -0.675 -11.913 -9.380 -3.313 -13.984 -2.533
“The moments were obtained as expectation values from ACCDS wavefunctions. The polarizabilities were found with DHF. Only symmetry-unique values are listed. The sign convention for the dipole moment is such that a positive charge on the positive z axis would have a positive dipole moment, and for the calculations, the oxygen atom was on the +z axis. So, the sense of the equilibrium dipole moment is C--o+ .
Maroulis and Thakkar has shown only a 3% correlation effect on the dipole polarizability and an 11% effect on the second hyperpolarizability.26 We have carried out property calculations for CO at the SCF level and at several correlated, coupled cluster levels. Calculations designated “ACCD” used the approximate double substitution coupled cluster treatmente2’ This approxiamtion has also been considered by Jankowski and Paldus under the label ACP-D45.28 ACCD, relative to the conventional double substitution coupled cluster (CCD) t ~ a t m e n t , ~ is ’ ~a~neglect of certain small Hamiltonian matrix elements of two types that tend to be of opposite sign and often of comparable size. There have been several examinations, both formal and applied, of the quality of the a p p r o ~ i m a t i o n , ~ and ~ ” ~ in our experience, it has proved quite faithful to CCD. Calculations designated “ACCDS” include single substitutions via a linearized, optimum procedure.40 Calculations designated with “B.O.” used Brueckner orbitals rather than SCF orbitals for the reference configuration. The Brueckner orbitals are those for which the expansion coefficients of the singly substituted configurations are identically zero, and they are found by an iterative procedure using the matrix oriented scheme for coupled cluster wavefunctions of Chiles and Dykstraam This scheme was the first use of Brueckner orbitals in coupled cluster wavefunctions, and it has been followed with other applications to bond breaking and properties [see, for example, refs 41-43]. (26) Maroulis, G.; Thakkar, A. J. J . Chem. Phys. 1990, 93, 652. (27) Chiles, R. A.; Dykstra, C. E. Chem. Phys. Lett. 1981,80, 69. Bachrach, s. M.; Chiles, R. A.; Dykstra, C. E. J . Chem. Phys. 1981, 75,2270. (28) Jankowski, K.; Paldus, J. Int. J . Quantum Chem. 1980, 18, 1243. (29) Cizek, J. J . Chem. Phys. 1966,45,4256; Adv. Chem. Phys. 1%9,14, 35. (30) Cizek, J.; Paldus, J.; Sroubkova, L. Int. J . Quantum Chem. 1969, 3, 149. (31) Hurley, A. C. Electron Correlation in Small Molecules; Academic: New York, 1976. (32) Bartlett, R. J.; Purvis, G. D. Int. J . Quantum Chem. 1978, 14, 561. (33) Lindgren, I. Int. J . Quantum Chem., Symp. 1978, 12, 33. (34) Bartlett, R. J. Annu. Reu. Phys. Chem. 1981, 32, 359. (35) Heriorski, B.; Monkhorst, H. J. Phys. Rev. A : Gen. Phys. 1981, 24, 1668. (36) Bartlett, R. J.; Paldus, J.; Dykstra, C. E. In Advanced Theories and Computational Approaches to the Electronic Structure of Molecules; Reidel: Dordrecht, 1984. (37) Saebo, S.; Pulay, P. Chem. Phys. Lett. 1986, 131, 384. (38) Dykstra, C. E.; Liu, S.-Y.;Daskalakis, M. F.; Lucia, J. P.; Takahashi, M. Chem. Phys. Lett. 1987, 137, 266. (39) Paldus, J.; Cizek, J.; Takahashi, M. Phys. Rev. A: Gen. Chem. 1984, 30, 2193. (40) Chiles, R. A.; Dykstra, C. E. J . Chem. Phys. 1981, 74, 4544. (41) Jasien, P. G.; Dykstra, C. E. Int. J . Quantum Chem., Symp. 1983, 17, 289.
Parish et al. Recently the use of Brueckner orbitals with double substitution coupled cluster wavefunctions was given its own designation, “BD”, by Handy et a1.,44who have nicely advanced the usefulness of this idea. Electrical properties, the permanent multipole moments, multipole polarizabilities, and multipole hyperpolarizabilities, were obtained analytically at the SCF level with the derivative Hartree-Fock (DHF) For correlated wavefunctions, properties were obtained by finite field calculations. Comparison of the corresponding SCF-level finite field results with analytical DHF results was used to assess the numerid accuracy of the finite field treatment at correlated levels. Basis set effects were considered by carrying out calculations with a large number of bases (see Appendix). Table I gives the set of properties for CO at the equilibrium that were judged the most reliable; these were used in the electrical representation of CO within the MMC model. Details of the calculations are given in the Appendix, but there are certain conclusions to be mentioned. (1) Property convergence with respect to basis set quality requires diffuse functions of both valence and polarization type, but 4f functions have only a small effect on first and second moment electrical properties. (2) Correlation has a small effect (6%) on the dipole polarizability in the region within 0.05 A of the equilibrium, though basis set incompleteness can exaggerate this. Correlation has a small effect (
