6284
J. Phys. Chem. 1996, 100, 6284-6287
Basis Set and Correlation Effects on Computed Lithium Ion Affinities† Janet E. Del Bene Department of Chemistry, Youngstown State UniVersity, Youngstown, Ohio 44555 ReceiVed: September 25, 1995; In Final Form: NoVember 29, 1995X
Ab initio calculations have been performed to investigate the basis set and correlation energy dependence of computed lithium ion affinities of a series of first- and second-row neutral bases (NH3, H2O, HF, HCN, CO, PH3, H2S, HCl) and of the corresponding anions which result from the loss of H+. The basis set dependence was evaluated at fourth-order many-body Møller-Plesset perturbation theory [MBPT(4) ) MP4], using the Dunning correlation-consistent polarized split-valence basis sets (cc-pVXZ, where X ) D for double, T for triple, and Q for quadruple split) and these sets augmented with diffuse functions on atoms other than H and Li (aug′-cc-pVXZ). The presence of diffuse functions in the basis set lowers computed Li+ affinities and reduces the basis set superposition error. Computed aug′-cc-pVXZ Li+ affinities converge with increasing basis set size, with satisfactory convergence occurring at aug′-cc-pVTZ. Comparison with CCSD(T) results indicates that the Møller-Plesset expansion appears to be converging except for the Li+ affinities of the anionic first-row bases NH2-, OH-, and F-.
Introduction There have appeared in the recent literature several studies of interactions of cations with bases.1-3 Feller et al.1 investigated complexes of Li+ with H2O clusters, with the cluster size ranging from 1 to 6. This study employed large Gaussian basis sets and several different correlation treatments. Magnusson2 investigated the binding of Li+, Na+, K+, Mg2+, and Ca2+ to the bases H2O, NH3, H2S, and PH3 using 6-31+G(d) and 6-311+G(d,p) basis sets. Subsequently, Glendening and Feller3 examined cation-water interactions in water clusters with various alkali metal cations. All three studies report binding energies for Li+ with a single H2O molecule. These energies differ, depending on the basis set, the level of correlation treatment, and the geometries used. A continuing research interest in this laboratory is the basis set and correlation energy dependence of computed acid-base interaction energies.4 Recently, studies of hydrogen bond energies of neutral, positive ion, and negative ion complexes5 and of proton affinities of neutral and negative ion bases6 were carried out. The basis sets employed for these studies were the Dunning correlation-consistent polarized split-valence basis sets7 (cc-pVXZ, where X ) D for double, T for triple, Q for quadruple, and 5 for quintuple split) and these basis sets augmented with diffuse functions on nonhydrogen atoms (aug′cc-pVXZ). The Dunning basis sets were chosen because they systematically expand both the valence space and the polarization space of the atoms. These studies provided further evidence that diffuse functions on nonhydrogen atoms are needed to lower computed interaction energies and bring them into better agreement with experimental data, and to significantly reduce the basis set superposition error at correlated levels of theory. Computed interaction energies were shown to converge with increasing basis set size. In the present work, the investigation of the basis-set dependence of interaction energies will be extended to Li+ affinities. It has also been demonstrated that the Møller-Plesset expansion may not be sufficiently converged at fourth order to provide reliable hydrogen bond energies of negative ion † Dedicated to Dr. Isaiah Shavitt, my teacher, research collaborator, and friend, in recognition of his seminal contributions to quantum chemistry. X Abstract published in AdVance ACS Abstracts, March 15, 1996.
0022-3654/96/20100-6284$12.00/0
complexes and proton affinities of anionic bases.5,6 Therefore, in this study correlated Li+ affinities of both neutral and anionic bases have also been computed at MP2, MP4, and CCSD(T) with the aug′-cc-pVTZ basis set. The results of these calculations provide the data necessary to evaluate the correlationenergy dependence of computed Li+ affinities and the degree to which the MP expansion has converged at fourth order. Methods The structures of the neutral bases NH3, H2O, HF, HCN, CO, PH3, H2S, and HCl and the corresponding anions NH2-, OH-, F-, CN-, PH2-, SH-, and Cl- had been optimized previously at second-order many-body Møller-Plesset perturbation theory8-11 [MBPT(2) ) MP2] using the split-valence 6-31+G(d,p) basis set with diffuse functions on nonhydrogen atoms.12-15 The Li+ complexes of these bases were fully optimized at the same level of theory for this study. Vibrational frequencies were computed to ensure that all structures correspond to equilibrium structures on the appropriate potential energy surfaces and to evaluate zeropoint and thermal vibrational energies. Complexes of CO and CN- with Li+ bonded at both atoms are included, as well as a T-shaped LiCN complex which also corresponds to a local minimum on the surface. Single-point calculations at the optimized MP2/6-31+G(d,p) geometries were carried out at second-order Møller-Plesset perturbation theory and at full fourth order including triples [MBPT(4) ) MP4SDTQ ) MP4], using the Dunning correlation-consistent split-valence basis sets (cc-pVXZ) and these basis sets augmented with diffuse functions on all atoms except hydrogen and lithium.7 (That diffuse functions on hydrogen are not significant has been demonstrated previously.4) Because the lithium orbitals in the cc-pVXZ basis sets are diffuse and since Li is positively charged, no diffuse functions were included on Li.1,3 MP4 calculations were also carried out with two diffuse-truncated basis sets: aug′-cc-pVTZ(-f), which is aug′cc-pVTZ minus diffuse f functions, and aug′-cc-pVTZ(-df), which is aug′-cc-pVTZ minus diffuse d and f. Correlated Li+ affinities have also been obtained at the CCSD(T) level of theory. CCSD(T) is an infinite-order coupledcluster correlation method which includes all single and double excitations and noniterative triples.16,17 The CCSD(T) calcula© 1996 American Chemical Society
Computed Lithium Ion Affinities
J. Phys. Chem., Vol. 100, No. 15, 1996 6285
TABLE 1: MP4 Electronic Li+ Affinities (kcal/mol) as a Function of Basis Seta cc-pV
aug′-cc-pV
DZ
TZ
45.4 (45.8) 41.6 29.9 36.1
41.1 (41.2) 36.3 24.5 35.6
H2S HCl NH2OHFCN- (at N) CN- (at C) CN- (T)
13.9 17.4 25.0 (25.4) 24.4 16.9 218.2 231.6 227.7 163.1 160.3 164.3
11.4 16.9 24.7 (25.0) 23.2 16.5 202.8 212.0 207.7 155.3 153.4 155.7
(24.9) 22.8 16.0 194.6 201.5 197.0 151.7 149.8 151.3
PH2SHCl-
165.3 168.8 166.1
157.1 159.6 160.4
152.3 155.1 155.9
NH3 H2O HF HCN CO (at O) CO (at C) PH3
QZ (39.8) 34.8 23.1 35.5 11.2 16.5
DZ
TZ
38.4 (38.6) 32.9 21.3 34.3 (34.3) 11.1 15.5 23.6 (24.1) 22.1 15.0 177.4 181.3 177.4 145.9 143.9 145.3 (144.8) 146.6 148.2 148.6
38.6 (38.7) 33.1 21.6 35.0 (35.1) 10.9 16.3 24.4 (24.6) 22.4 15.7 179.3 183.5 179.9 147.7 146.0 147.5 (147.1) 147.7 150.4 151.7
QZ (38.9) 33.4 21.9 (35.2) 11.0 16.2 (24.8) 22.5 15.8 179.6 184.0 180.7b 148.0 146.2 (147.4) 147.9 150.7 152.1
a MP2 values given in parentheses. b The aug′-cc-pV5Z Li+ affinity is 180.5 kcal/mol. See ref 22.
Figure 1. MP4 Li+ affinity of F- computed with cc-pVXZ and aug′cc-pVXZ basis sets. Note the change of scale for cc-pVXZ and aug′cc-pVXZ. (s) Uncorrected Li+ affinity; (- -) counterpoise-corrected Li+ affinity.
tions were done with the aug′-cc-pVTZ basis set. Li+ affinities counterpoise corrected18 for the basis set superposition error have also been obtained for F- and HF. All correlation calculations were done freezing electrons below the valence shells in the Hartree-Fock MO’s. Li+ affinities were computed as -∆E for the reaction
Li+ + B f BLi+
(1)
CCSD(T)/aug′-cc-pVTZ Li+ affinities have been converted to reaction enthalpies for eq 1 by adding MP2/6-31+G(d,p) zeropoint vibrational energy contributions and the remaining thermal terms.19 These computed enthalpies [-∆H298] may then be compared directly with experimental values. The calculations reported in this paper were carried out on the Cray Y-MP8/864 computer using the Gaussian 9220 and ACES221 computer programs. Results and Discussion cc-pVXZ vs aug′-cc-pVXZ. Table 1 lists the computed Li+ affinities obtained with cc-pVXZ and aug′-cc-pVXZ basis sets. Computed Li+ affinities are too high when diffuse functions are not present in the basis set. For the anions NH2-, OH-, and F-, computed cc-pVQZ affinities are about 15-18 kcal/ mol greater than aug′-cc-pVTZ affinities, even though the former basis set is much larger than the latter (55 and 30 basis functions on first-row atoms and H, respectively, versus 46 and 14, respectively). For CN- and the second-row anionic bases, the differences are smaller, but the cc-pVQZ values are still 4-5 kcal/mol greater than the aug′-cc-pVTZ affinities. For neutral bases smaller differences are found between cc-pVQZ and aug′cc-pVTZ affinities, but the cc-pVQZ affinities are still greater by a few tenths to 2 kcal/mol. The presence of diffuse functions also leads to a significant decrease in the basis set superposition error as estimated by the counterpoise correction.18 This is illustrated in Figures 1 and 2, which show the MP4 corrected and uncorrected Li+ affinities with the cc-pVXZ and aug′-cc-pVXZ basis sets for F- and HF,
Figure 2. MP4 Li+ affinity of HF computed with cc-pVXZ and aug′cc-pVXZ basis sets. (s) Uncorrected Li+ affinity; (- -) counterpoisecorrected Li+ affinity.
respectively. Without diffuse functions, the counterpoise correction for F- is 40.4, 25.5, and 15.0 kcal/mol with the DZ, TZ, and QZ basis sets, respectively. With diffuse functions, these corrections are reduced to 0.9, 0.7, 0.4, and 0.1 kcal/mol at aug′-DZ, -TZ, -QZ, and -5Z,22 respectively. For HF, the counterpoise corrections to the Li+ affinities are not as large at 5.8, 2.9, and 1.2 kcal/mol with the cc-pVDZ, cc-pVTZ, and cc-pVQZ basis sets, respectively. However, when diffuse functions are present, the counterpoise corrections are even smaller at 0.6, 0.3, and 0.2 kcal/mol, for the augmented DZ, TZ, and QZ basis sets, respectively. It is important to note that for both HF and F- the uncorrected aug′-cc-pVTZ Li+ affinities are nearer the interval between the corrected and uncorrected aug′-cc-pVQZ values than are the counterpoise-corrected values.
6286 J. Phys. Chem., Vol. 100, No. 15, 1996
Del Bene
TABLE 2: MP4 Electronic Li+ Affinities (kcal/mol) Computed with Diffused-Truncated aug′-cc-pVTZ Basis Sets
NH3 H2O HF HCN CO (at O) CO (at C) PH3 H2S HCl NH2OHFCN- (at N) CN- (at C) CN- (T) PH2SHCl-
aug′-ccpVTZ
aug′-ccpVTZ(-f)a
aug′-ccpVTZ(-df)b
38.6 33.1 21.6 35.0 10.9 16.3 24.4 22.4 15.7 179.3 183.5 179.9 147.7 146.0 147.5 147.7 150.4 151.7
38.6 33.0 21.5 35.0 10.8 16.4 24.6 22.7 15.9 179.5 183.5 179.7 147.8 146.3 147.7 148.5 151.1 152.4
39.1 33.5 21.7 35.1 10.8 16.4 24.7 22.9 16.2 181.5 185.6 181.8 148.3 146.8 148.4 149.7 152.7 154.2
a
aug′-cc-pVTZ minus the diffuse f functions. b aug′-cc-pVTZ minus the diffuse d and f functions.
Li+
Subsequently, only affinities computed with aug′-cc-pVXZ basis sets without the counterpoise correction will be discussed.1,5,6 aug′-cc-pVXZ Convergence of Li+ Affinities. The data of Table 1 also show that for the neutral and anionic bases computed MP4 Li+ affinities appear to converge with increasing basis set size.23 For the neutral bases, aug′-cc-pVDZ Li+ affinities are within 1 kcal/mol of aug′-cc-pVQZ values, while aug′-cc-pVTZ Li+ affinities differ from aug′-cc-pVQZ affinities by 0.3 kcal/mol or less. For the anionic bases, aug′-cc-pVDZ Li+ affinities are lower than aug′-cc-pVQZ affinities by about 2-3.5 kcal/mol. In contrast, aug′-cc-pVTZ affinities differ from aug′-cc-pVQZ affinities by 0.2-0.8 kcal/mol. The aug′-ccpVQZ Li+ affinity of F- is only 0.2 kcal/mol greater than the aug′-cc-pV5Z affinity.22 Thus, for both neutral and anionic bases, computed MP4 Li+ affinities converge with increasing basis set size using the aug′-cc-pVXZ basis sets, with satisfactory convergence occurring at aug′-cc-pVTZ. For the neutral bases, even aug′-cc-pVDZ Li+ affinities may be sufficiently converged. The Dunning aug′-cc-pVTZ basis set contains diffuse s, p, d, and f functions. In the interest of computational efficiency, it is appropriate to ask whether diffuse functions beyond s and p are required for the calculation of Li+ affinities. The data of Table 2 form the basis for making this assessment. For all of the neutral bases and for the anionic bases containing first-row atoms, removing the diffuse f functions changes computed Li+ affinities by 0.3 kcal/mol or less. However, for the secondrow anionic bases, removing diffuse f functions increases computed Li+ affinities by 0.7-0.8 kcal/mol. For the neutral bases, removing both diffuse d and f functions also has a relatively small effect, changing computed Li+ affinities by no more than 0.5 kcal/mol. However, for the anionic bases, removal of diffuse d functions in addition to f significantly increases Li+ affinities by 1-2.5 kcal/mol. Thus, for first-row anionic bases, diffuse d functions should be retained in the aug′cc-pVTZ basis set, while for second-row anions diffuse d and f functions should be retained. Electron Correlation Effects. The data of Table 3 show that inclusion of electron correlation usually lowers computed Li+ affinities of both neutral and anionic bases, but there are exceptions. For CO and CN- with Li+ bonded at C, electron correlation evaluated at MP4 increases Hartree-Fock Li+
TABLE 3: Hartree-Fock and Correlated Li+ Affinities (kcal/mol) with the aug′-cc-pVTZ Basis Set NH3 H 2O HF HCN CO (at O) CO (at C) PH3 H 2S HCl NH2OHFCN- (at N) CN- (at C) CN- (T) PH2SHCl-
HF
MP2
MP4
CCSD(T)
39.8 35.2 23.4 38.1 15.3 13.4 26.9 23.2 15.8 185.4 190.9 185.2 152.7 145.3 149.4 147.7 150.8 151.9
38.7 33.3 21.8 35.1 10.1 16.8 24.6 22.5 15.7 179.3 184.2 180.6 146.8 146.4 147.1 147.4 150.1 151.5
38.6 33.1 21.6 35.0 10.9 16.3 24.4 22.4 15.7 179.3 183.5 179.9 147.7 146.0 147.5 147.7 150.4 151.7
38.7 33.3 21.9 35.2 11.8 15.6 24.4 22.4 15.7 180.3 185.3 181.5 148.3 145.9 147.9 147.8 150.5 151.8
TABLE 4: Li+ Affinities (Negative Binding Enthalpies, kcal/mol) at 298 Ka,b NH3 H2O HF HCN CO (at O) CO (at C) PH3 H2S HCl
37.4 (39.1) 32.4 (34.0) 21.6 34.4 (36.4) 11.3 15.0 23.4 21.7 15.5
NH2OHFCN- (at N) CN- (at C) CN- (T) PH2SHCl-
178.5 183.6 181.2 (182 ( 5) 147.4 145.1 147.4 147.0 149.9 151.7 (153 ( 3)
a Based on CCSD(T)/aug′-cc-pVTZ electronic energies and unscaled MP2/6-31+G(d,p) zero-point and thermal vibrational energies. b Experimental data given in parentheses. Data for neutrals from ref 24; data for anions from ref 25.
affinities by 2.9 and 0.7 kcal/mol, respectively. For HCl and the second-row anionic bases PH2-, SH-, and Cl-, the effect of correlation is negligible. The MP expansion for the Li+ affinities appears to be well-behaved for the neutral bases NH3, H2O, HF, HCN, PH3, H2S, and HCl and for the anionic bases PH2-, SH-, and Cl-, since computed MP2 and MP4 affinities agree with CCSD(T) affinities to within 0.4 kcal/mol. For CO and CN-, the MP expansion appears to be converging toward the CCSD(T) Li+ affinities, although differences between MP4 and CCSD(T) range from 0.4 to 0.9 kcal/mol. The MP expansion does not appear to be converging for the anionic bases of the first row. Computed MP2 Li+ affinities of NH2-, OH-, and F- are lower than CCSD(T) affinities by 1.0, 1.1, and 0.9 kcal/mol, while computed MP4 affinities are lower by 1.0, 1.8, and 1.6 kcal/mol, respectively. For these bases an infinite-order treatment of correlation effects on Li+ affinities appears to be required. A similar observation was made previously for the proton affinities of these anions.6 Comparison with Experimental Data. Table 4 reports the computed Li+ affinities [-∆H298 for reaction 1] based on CCSD(T)/aug′-cc-pVTZ electronic energies and MP2/6-31+G(d,p) zero-point and thermal vibrational energies. Only a few experimental results are available for comparison, and these are also included in Table 4. The computed CCSD(T)/aug′-ccpVTZ Li+ affinities of the anions F- and Cl- are in good agreement with experimental affinities.24 For the neutral bases, the experimental data indicate that basicity toward Li+ increases in the order H2O < HCN < NH3, with HCN more basic than H2O by 2.4 kcal/mol and NH3 more basic than HCN by 2.7 kcal/mol. The computed values follow the same order, with HCN more basic than H2O by 2.0 kcal/mol and NH3 more basic than HCN by 3.0 kcal/mol. However, the computed affinities
Computed Lithium Ion Affinities are lower than the experimental ones by about 2 kcal/mol, suggesting that the absolute Li+ affinity scale may need to be reexamined. The trends in computed Li+ affinities are noteworthy. The Li+ affinities of neutral first-row bases are greater than those of the corresponding second-row bases, with the orders NH3 > H2O > HF and PH3 > H2S > HCl. These affinities show a significant dependence on the nature of the heavy atom, with differences of 16 kcal/mol among first-row bases and 8 kcal/ mol among second-row bases. The neutral base CO has the lowest Li+ affinity, with Li+ association at C preferred over association at O by about 4 kcal/mol. Relationships among the Li+ affinities of anionic bases are quite different. Anions of the first row still have higher Li+ affinities than those of the corresponding second row, but the order is different [OH- > F- > NH2- versus PH2- > SH- > Cl-]. These affinities show a lesser dependence on the nature of the heavy atom, with a variation of about 3 kcal/mol among first-row anions and 5 kcal/mol among second-row anions, even though the absolute Li+ affinities are significantly larger than those of the corresponding neutral bases. The Li+ affinity of CN- exhibits little dependence on the site of association, since the three isomers of LiCN differ in stability by only 2 kcal/ mol. Conclusions The following conclusions are supported by the data obtained in this study. 1. Computed MP4/aug′-cc-pVXZ Li+ affinities converge with increasing basis set size, with satisfactory convergence occurring at aug′-cc-pVTZ. For neutral bases, even aug′-ccpVDZ affinities appear to be sufficiently converged. Previous studies5,6 have shown that computed hydrogen bond energies and proton affinities are also sufficiently converged at aug′-ccpVTZ. Hence, aug′-cc-pVTZ is the recommended basis set for the calculation of such acid-base interaction energies. 2. Diffuse functions are required in the basis set to reduce computed Li+ affinities and lower the basis set superposition error. 3. Diffuse functions beyond s and p are not required in the aug′-cc-pVTZ basis set for calculation of the Li+ affinities of neutral bases. For the anionic first-row bases, diffuse d functions are needed, while, for the anionic second-row bases, both diffuse d and diffuse f functions are required. 4. The inclusion of electron correlation usually lowers computed Li+ affinities. Exceptions are CO and CN- with Li+ bonded at C, where correlation increases Li+ affinities, and HCl and the second-row anionic bases, where correlation effects are negligible. 5. The Møller-Plesset expansion is well-behaved and essentially converged relative to CCSD(T) Li+ affinities except for CO and CN-, in which cases the MP expansion appears to be converging more slowly, and for the anionic first-row bases, where the MP expansion does not appear to be converging at MP4. 6. Computed Li+ affinities at CCSD(T)/aug′-cc-pVTZ with MP2/6-31+G(d,p) zero-point and thermal corrections (-∆H298 values) are in agreement with experimental Li+ affinities for
J. Phys. Chem., Vol. 100, No. 15, 1996 6287 the anions F- and Cl-. Although experimental trends among Li+ affinities of neutral bases are reproduced, the computed affinities are about 2 kcal/mol lower than the experimental values. Acknowledgment. Part of this work was carried out at the Ohio Supercomputer Center (OSC). The support of OSC is gratefully acknowledged. Thanks are also due to Dr. Thom Dunning, Jr., for providing the Li basis sets prior to publication. References and Notes (1) Feller, D.; Glendening, E. D.; Kendall, R. A.; Peterson, K. A. J. Chem. Phys. 1994, 100, 4981. (2) Magnusson, E. J. Phys. Chem. 1994, 98, 12558. (3) Glendening, E. D.; Feller, D. J. Phys. Chem. 1995, 99, 3060. (4) (a) Del Bene, J. E. Chem. Phys. Lett. 1983, 94, 213; J. Comput. Chem. 1984, 5, 381; J. Comput. Chem. 1985, 6, 296; J. Comput. Chem. 1986, 7, 259; J. Chem. Phys. 1987, 86, 2110; J. Comput. Chem. 1987, 8, 810; Int. J. Quantum Chem., Quantum Bio. Symp. 1987, 14, 27. (b) Frisch, M. J.; Del Bene, J. E.; Binkley, J. S.; Schaefer, H. F. J. Chem. Phys. 1986, 84, 2279. (c) Del Bene, J. E.; Shavitt, I. J. Phys. Chem. 1990, 94, 5514; Int. J. Quantum Chem., Quantum Chem. Symp. 1990, 24, 455. (5) Del Bene, J. E.; Shavitt, I. J. Mol. Struct. (THEOCHEM) 1994, 307, 27. (6) Del Bene, J. E. J. Phys. Chem. 1993, 97, 107. (7) Dunning, T. H., Jr. J. Chem. Phys. 1989, 90, 1007. Kendall, R. A.; Dunning, T. H., Jr.; Harrison, R. J. J. Chem. Phys. 1992, 96, 6796. Woon, D. E.; Dunning, T. H., Jr. J. Chem. Phys. 1993, 98, 1358. (8) Pople, J. A.; Binkley, J. S.; Seeger, R. Int. J. Quantum Chem., Quantum Chem. Symp. 1976, 10, 1. (9) Krishnan, R.; Pople, J. A. Int. J. Quantum Chem. 1978, 14, 91. (10) Bartlett, R. J.; Silver, D. M. J. Chem. Phys. 1975, 62, 3258. (11) Bartlett, R. J.; Purvis, G. D. Int. J. Quantum Chem. 1978, 14, 561. (12) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973, 28, 213. (13) Dill, J. D.; Pople, J. A. J. Chem. Phys. 1975, 62, 2921. (14) Spitznagel, G. W.; Clark, T.; Chandrasekhar, J.; Schleyer, P. v. R. J. Comput. Chem. 1982, 3, 3633. (15) Clark, T.; Chandrasekhar, G. W.; Spitznagel, G. W.; Schleyer, P. v. R. J. Comput. Chem. 1983, 4, 294. (16) Purvis, G. D., III; Bartlett, R. J. J. Chem. Phys. 1982, 76, 1910. (17) Urban, M.; Noga, J.; Cole, S. J.; Bartlett, R. J. J. Chem. Phys. 1985, 83, 4041. (18) Boys, S. F.; Bernardi, F. Mol. Phys. 1970, 19, 553. (19) Del Bene, J. E. In Molecular Structure and Energetics; Greenberg, A., Liebman, J. F., Eds.; Springer-Verlag Publishing Company, Inc.: Deerfield Beach, FL, 1986; Vol. I, pp 319-349. (20) Frisch, M. J.; Trucks, G. W.; Head-Gordon, M.; Gill, P. M. W.; Wong, M. W.; Foresman, J. B.; Johnson, B. G.; Schlegel, H. B.; Robb, M. A.; Replogle, E. S.; Gomperts, R.; Andres, J. L.; Raghavachari, K.; Binkley, J. S.; Gonzalez, C.; Martin, R. L.; Fox, D. J.; DeFrees, D. J.; Baker, J.; Stewart, J. J. P.; Pople, J. A. Gaussian 92; Gaussian, Inc.: Pittsburgh, PA, 1992. (21) ACES2 is a new program package from the Quantum Theory Project of the University of Florida. The SCF, integral transformation, and correlation energy codes in this package were written by J. F. Stanton, J. Gauss, J. D. Watts, W. J. Lauderdale, and R. J. Bartlett. [See, e.g.: Stanton, J. F.; Gauss, J.; Watts, J. D.; Bartlett, R. J. J. Chem. Phys. 1991, 94, 4334.] The package also includes the VMOL integral program written by P. R. Taylor and J. Almlo¨f. (22) The Li+ affinity of F- computed with the full aug′-cc-pV5Z basis set on F and cc-pVQZ on Li is 180.5 kcal/mol. The counterpoise corrected value is 180.4 kcal/mol. (23) The calculation of Li+ affinities at MP4/aug′-cc-pVQZ is expensive computationally. For NH3, HCN, PH3, and the T-structure of LiCN only MP2 affinities were obtained at aug′-cc-pVQZ. These are given in parentheses in Table 1. Variations in Li+ affinities in going from aug′-ccpVDZ to aug′-cc-pVTZ to aug′-cc-pVQZ are similar at MP2 and MP4. (24) Woodin, R. L. Beauchamp, J. L. J. Am. Chem. Soc. 1978, 100, 501. (25) Weast, R. C., Astle, M. J., Eds. CRC Handbook of Chemistry and Physics; CRC Press: Boca Raton, FL, 1982.
JP9528424
