基于支撑向量机方法的有机化合物的生成Gibbs自由能的预测

基于支撑向量机方法的有机化合物的生成Gibbs自由能的预测;支撑向量机;多元线形回归;吉布斯自由能     

Stabilisation energy of C(6)H(6)...C(6)X(6) (X = F, Cl, Br, I, CN) complexes: complete basis set limit calculations at MP2 and CCSD(T) levels

Stabilisation energies of stacked structures of C(6)H(6)...C(6)X(6) (X = F, Cl, Br, CN) complexes were determined at the CCSD(T) complete basis set (CBS) limit level. These energies were constructed from MP2/CBS stabilisation energies and a CCSD(T) correction term determined with a medium basis set (6-31G**). The former energies were extrapolated using the two-point formula of Helgaker et al. from aug-cc-pVDZ and aug-cc-pVTZ Hartree-Fock energies and MP2 correlation energies. The CCSD(T) correction term is systematically repulsive. The final CCSD(T)/CBS stabilisation energies are large, considerably larger than previously calculated and increase in the series as follows: hexafluorobenzene (6.3 kcal mol(-1)), hexachlorobenzene (8.8 kcal mol(-1)), hexabromobenzene (8.1 kcal mol(-1)) and hexacyanobenzene (11.0 kcal mol(-1)). MP2/SDD** relativistic calculations performed for all complexes mentioned and also for benzene[dot dot dot]hexaiodobenzene have clearly shown that due to relativistic effects the stabilisation energy of the hexaiodobenzene complex is lower than that of hexabromobenzene complex. The decomposition of the total interaction energy to physically defined energy components was made by using the symmetry adapted perturbation treatment (SAPT). The main stabilisation contribution for all complexes investigated is due to London dispersion energy, with the induction term being smaller. Electrostatic and induction terms which are attractive are compensated by their exchange counterparts. The stacked motif in the complexes studied is very stable and might thus be valuable as a supramolecular synthon.     

Complexes of ammonia with propane and cyclopropane: electrostatic guidelines for ab initio treatment

A model based on the molecular electrostatic potential (MESP) is employed for the investigation of structures and energies of complexes of ammonia with propane and cyclopropane. The electrostatic model geometries are employed as starting points for an ab initio investigation at the self-consistent field and second-order M?ller-Plesset (MP2) levels. The most stable structures of C₃H₆..NH₃ and C₃H₈..NH₃ complexes have the interaction energies of 10.07 kJ/mol and 8.15 kJ/mol, respectively, at the MP2/6-31G(d,p) level. The energy rank order of the structures is not altered with the use of the 6-31++G(d,p) basis set, and the basis␣set superposition error has little effect. The interaction energy decomposition analysis shows that the electrostatic component is dominant over the other ones. MESP topography thus seems to offer valuable hints for predicting the structures of weakly bonded complexes. Received: 8 July 1998 / Accepted: 4 August 1998 / Published online: 2 November 1998     

尿素与鸟嘌呤相互作用的DFT研究

采用B3LYP／6—311＋G^＋方法对鸟嘌呤-尿素复合物氢键相互作朋体系进行了研究,并对该复合物的几何构型及结合能（BSSE）进行了计算．此外,采用从静电势导出原子净电荷的chelpg方法分析了体系中的电荷转移和利用分子中的原子理论（AIM）方法对相互作用的本质进行了分析．结果一共得到五个稳定的复合物构型,其中A5是最稳定的,结合能为-73．95kJ／mol．     

Parameterization of a B3LYP specific correction for non-covalent interactions and basis set superposition error on a gigantic dataset of CCSD(T) quality non-covalent interaction energies

A vast number of non-covalent interaction energies at the counterpoise corrected CCSD(T) level have been collected from the literature to build a diverse new dataset. The whole dataset, which consists of 2027 CCSD(T) energies, includes most of the published data at this level. A large subset of the data was then used to train a novel, B3LYP specific, empirical correction scheme for non-covalent interactions and basis set superposition error (abbreviated as B3LYP-MM). Results obtained with our new correction scheme were directly compared to benchmark results obtained with B3LYP-D3(1) and M06-2X(2) (two popular density functions designed specifically to accurately model non-covalent interactions). For non-covalent complexes dominated by dispersion or dipole-dipole interactions all three tested methods give accurate results with the medium size aug-cc-pVDZ(3-6) basis set with MUE's of 0.27 (B3LYP-MM), 0.32 (B3LYP-D3) and 0.47 kcal/mol (M06-2X) (with explicit counterpoise corrections). These results validate both B3LYP-D3 and M06-2X for interactions of this type using a much larger data set than was presented in prior work. However, our new dispersion correction scheme shows some clear advantages for dispersion and dipole-dipole dominated complexes with the small LACVP* basis set, which is very popular in use due to its low associated computational cost: The MUE for B3LYP-MM with the LACVP* basis set for this subset of complexes (without explicit counterpoise corrections) is only 0.28 kcal/mol, compared to 0.65 kcal/mol for M06-2X or 1.16 kcal/mol for B3LYP-D3. Additionally, our new correction scheme also shows major improvements in accuracy for hydrogen-bonded systems and for systems involving ionic interactions, for example cation-π interactions. Compared to B3LYP-D3 and M06-2X, we also find that our new B3LYP-MM correction scheme gives results of higher or equal accuracy for a large dataset of conformer energies of di- and tripeptides, sugars, and cysteine.     

四唑负离子与脒正离子复合物稳定性的理论研究

采用密度泛函B3LYP/6-31+G(d,p) 方法和自洽反应场极化连续模型(PCM)研究四唑负离子与脒类(乙脒或苄脒)正离子形成的两种形式的复合物(末端和侧端)及甲酸根负离子与脒类(乙脒或苄脒)正离子形成的复合物在气相和二甲亚砜（DMSO）溶剂中的稳定性。在气相中,四唑-乙脒和四唑-苄脒复合物的相互作用能(∆E)末端分别比侧端的大3.56和3.72 kJ/mol,表明末端复合物稍占优势。甲酸与乙脒和苄脒的复合物的相互作用能(∆E)分别比四唑与乙脒和苄脒的复合物的大59.35和58.99 kJ/mol,表明脒与甲酸形成复合物时相互作用更强。溶剂DMSO的作用使得所有复合物的相互作用能变小,但脒与四唑的相互作用仍比脒与甲酸的弱。前者的结合常数与后者的相比只有1/315（乙脒）和1/218（苄脒）,这与实验结果相一致。     

Effect of substituents on the stabilities of multiply-substituted carbon-centered radicals

The bond dissociation energies (BDEs) and radical stabilization energies (RSEs) which result from 166 reactions that lead to carbon-centered radicals of the type ˙CH(2)X, ˙CHXY and ˙CXYZ, where X, Y and Z are any of the fourteen substituents H, F, Cl, NH(2), OH, SH, CH[double bond, length as m-dash]CH(2), C[triple bond, length as m-dash]CH, BH(2), CHO, COOH, CN, CH(3), and CF(3), were calculated using spin-restricted and -unrestricted variants of the double-hybrid B2-PLYP method with the 6-311+G(3df,2p) basis set. The interactions of substituents X, Y, and Z in both the radicals (˙CXYZ) and in the precursor closed-shell molecules (CHXYZ), as well as the extent of additivity of such interactions, were investigated by calculating radical interaction energies (RIEs), molecule interaction energies (MIEs), and deviations from additivity of RSEs (DARSEs) for a set of 152 reactions that lead to di- (˙CHXY) and tri- (˙CXYZ) substituted carbon-centered radicals. The pairwise quantities describing the effects of pairs of substituents in trisubstituted systems, namely pairwise MIEs (PMIEs), pairwise RIEs (PRIEs) and deviations from pairwise additivity of RSEs (DPARSEs), were also calculated for the set of 61 reactions that lead to trisubstituted radicals (˙CXYZ). Both ROB2-PLYP and UB2-PLYP were found to perform quite well in predicting the quantities related to the stabilities of carbon-centered radicals when compared with available experimental data and with the results obtained from the high-level composite method G3X(MP2)-RAD. Particular selections of substituents or combinations of substituents from the current test set were found to lead to specially stable radicals, increasing the RSEs to a maximum of +68.2 kJ mol(-1) for monosubstituted radicals ˙CH(2)X (X = CH[double bond, length as m-dash]CH(2)), +131.7 kJ mol(-1) for disubstituted radicals ˙CHXY (X = NH(2), Y = CHO), and +177.1 kJ mol(-1) for trisubstituted radicals ˙CXYZ (X = NH2, Y = Z = CHO).     

Binding affinities for models of biologically available potential Cu(II) ligands relevant to Alzheimer's disease: an ab initio study

A systematic study of the binding affinities of the model biological ligands X: = (CH3)2S, CH3S-, CH3NH2, 4-CH3-imidazole (MeImid), C6H5O-, and CH3CO2- to (NH3)i(H2O)3-iCu(II)-H2O (i = 3, 2, 1, 0) complexes has been carried out using quantum chemical calculations. Geometries have been obtained at the B3LYP/ 6-31G(d) level of theory, and binding energies, Delta, relative to H2O as a ligand, have been calculated at the B3LYP/6-311+G(2df,2p)//B3LYP/6-31G(d) level. Solvation effects have been included using the COSMO model, and the relative binding free energies in aqueous solution (Delta) have been determined at pH 7 for processes that are pH dependent. CH3S- (Delta = -16.0 to -53.5 kJ mol(-1)) and MeImid (Delta = -18.5 to -35.2 kJ mol(-1)) give the largest binding affinities for Cu(II). PhO- and (CH3)2S are poor ligands for Cu(II), Delta = 20.6 to -9.7 and 19.8 to -3.7 kJ mol(-1), respectively. The binding affinities for CH3NH2 range from -0.8 to -15.0 kJ mol(-1). CH3CO2- has Cu(II) binding affinities in the ranges Delta = -13.5 to -32.4 kJ mol(-1) if an adjacent OH bond is available for hydrogen bonding and Delta = 10.1 to -4.6 kJ mol(-1) if this interaction is not present. In the context of copper coordination by the Abeta peptide of Alzheimer's disease, the binding affinities suggest preferential binding of Cu(II) to the three histidine residues plus a lysine or the N-terminus. For a 3N1O Cu(II) ligand arrangement, it is more probable that the oxygen ligand comes from an aspartate/glutamate residue side chain than from the tyrosine at position 10. Methionine appears unlikely to be a Cu(II) ligand in Abeta.     

Ketene-ketenimine rearrangements in the gas phase and in polar media. 1,3-Migration intermediates and sequential transition states

[reaction: see text] Calculations of the activation barrier for the 1,3-shifts of substituents X in alpha-imidoylketenes 1 (HN=C(X)-CH=C=O), which interconverts them with alpha-oxoketenimines 3 (HN=C=CH-C(X)=O) via a four-membered cyclic transition state TS2 have been performed at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G* level. Substituents with accessible lone pairs have the lowest activation barriers for the 1,3-shift (halogens, OR, NR2). The corresponding activation barriers for the alpha-oxoketene-alpha-oxoketene rearrangement of 4 via TS5 are generally lower by 1-30 kJ/mol. A polar medium (acetonitrile, epsilon = 36.64) was simulated using the polarizable continuum (PCM) solvation model. The effect of the solvent field is a reduction of the activation barrier by an average of 12 kJ/mol. In the cases of 1,3-shifts of amino and dimethylamino groups, the stabilization of the transition state TS2 in a solvent field is so large that it becomes an intermediate, Int2, flanked by transition states (TS2' and TS2') that are due primarily to internal rotation of the amine functions, and secondarily to the 1,3-bonding interaction. In the case of the alpha-oxoketene-alpha-oxoketene rearrangement of 4, there is a corresponding intermediate Int5 for the 1,3-amine shift already in the gas phase.     

Electrophilic attack on sulfur-sulfur bonds: coordination of lithium cations to sulfur-rich molecules studied by ab initio MO methods

Complex formation between gaseous Li+ ions and sulfur-containing neutral ligands, such as H2S, Me2Sn (n = 1-5; Me = CH3) and various isomers of hexasulfur (S6), has been studied by ab initio MO calculations at the G3X(MP2) level of theory. Generally, the formation of LiS(n) heterocycles and clusters is preferred in these reactions. The binding energies of the cation in the 29 complexes investigated range from -88 kJ mol(-1) for [H2SLi]+ to -189 kJ mol(-1) for the most stable isomer of [Me2S5Li]+ which contains three-coordinate Li+. Of the various S6 ligands (chair, boat, prism, branched ring, and triplet chain structures), two isomeric complexes containing the S5==S ligand have the highest binding energies (-163+/-1 kJ mol(-1)). However, the global minimum structure of [LiS6]+ is of C(3v) symmetry with the six-membered S(6) homocycle in the well-known chair conformation and three Li--S bonds with a length of 256 pm (binding energy: -134 kJ mol(-1)). Relatively unstable isomers of S6 are stabilized by complex formation with Li+. The interaction between the cation and the S6 ligands is mainly attributed to ion-dipole attraction with a little charge transfer, except in cations containing the six sulfur atoms in the form of separated neutral S2, S3, or S4 units, as in [Li(S3)2]+ and [Li(S2)(S4)]+. In the two most stable isomers of the [LiS6]+ complexes, the number of S--S bonds is at maximum and the coordination number of Li+ is either 3 or 4. A topological analysis of all investigated complexes revealed that the Li--S bonds of lengths below 280 pm are characterized by a maximum electron-density path and closed-shell interaction.     

传统氢键(X—H…Y)还是X—H…π相互作用？ ——无机苯与卤化氢相互作用本质的量子化学研究

在MP2/6-311＋＋G**水平对无机苯(B3N3H6)与卤化氢HX (X＝F, Cl, Br, I)相互作用体系进行了系统研究. 结果表明在B3N3H6-HX (X＝F, Cl, Br, I)体系的平衡几何结构中, HX的H原子倾向于指向B3N3H6环上的N原子, 且从HF到HI相互作用强度依次减弱. 与苯-卤化氢体系比较, 除与HF相互作用B3N3H6较C6H6强外, 其余体系B3N3H6均较C6H6弱(结合能数值相差4 kJ/mol左右). 对称匹配微扰理论(SAPT)能量分解结果说明静电、诱导和色散力对描述B3N3H6-卤化氢体系的相互作用都很重要, 从HF到HI静电能占总吸引作用能的百分比逐渐减少, 色散能占总吸引作用能的百分比逐渐增加, 这种变化趋势与苯-卤化氢体系比较类似, 表明B3N3H6与卤化氢的相互作用随着卤素原子序数的递增, 传统氢键作用趋势减弱, X—H…π相互作用趋势增强.     

AB INITIO SCF MO STUDIES ON THE COMPLEXES BETWEEN CH_3OH AND H_2CO

<正> The interaction between CH3OH and H2CO has been studied by ab ini-tio method at the level of STO-3G and 6-311G basis sets. It has been found that there are two possible complexes; a hydrogen bonded complex CH3OH...CH2O(Ⅰ) and an electron donor-acceptor complex CH3OH.....OCH2(Ⅱ).The stabilization energies of (Ⅰ) and (Ⅱ) are 14. 6 and 3. 6kJ/mol (STO-3G results) or 25. 1 and 17. 1kJ/mol (6-311G results) respectively. The nature of these complexes has been discussed by using the energy decomposition scheme.     

Ab initio study of hydrogen-bond formation between aliphatic and phenolic hydroxy groups and selected amino acid side chains

Hydrogen bonding was studied in 24 pairs of isopropyl alcohol and phenol as one partner, and water and amino-acid mimics (methanol, acetamide, neutral and protonated imidazole, protonated methylalamine, methyl-guanidium cation, and acetate anion) as the other partner. MP2/6-31+G* and MP2/aug-cc-pvtz calculations were conducted in the gas phase and in a model continuum dielectric environment with dielectric constant of 15.0. Structures were optimized in the gas phase with both basis sets, and zero-point energies were calculated at the MP2/6-31+G* level. At the MP2/aug-cc-pvtz level, the BSSE values from the Boys-Bernardi counterpoise calculations amount to 10-20 and 5-10% of the uncorrected binding energies of the neutral and ionic complexes, respectively. The geometry distortion energy upon hydrogen-bond formation is up to 2 kcal/mol, with the exception of the most strongly bound complexes. The BSSE-corrected MP2/aug-cc-pvtz binding energy of -27.56 kcal/mol for the gas-phase acetate...phenol system has been classified as a short and strong hydrogen bond (SSHB). The CH3NH3+...isopropyl alcohol complex with binding energy of -22.54 kcal/mol approaches this classification. The complete basis set limit (CBS) for the binding energy was calculated for twelve and six complexes on the basis of standard and counterpoise-corrected geometry optimizations, respectively. The X...Y distances of the X-H...Y bridges differ by up to 0.03 A as calculated by the two methods, whereas the corresponding CBS energy values differ by up to 0.03 kcal/mol. Uncorrected MP2/aug-cc-pvtz hydrogen-bonding energies are more negative by up to 0.35 kcal/mol than the MP2/CBS values, and overestimate the CCSD(T)/CBS binding energies generally by up to 5% for the eight studied complexes in the gas phase. The uncorrected MP2/aug-cc-pvtz binding energies decreased (in absolute value) by 11-18 kcal/mol for the ionic species and by up to 5 kcal/mol for the neutral complexes when the electrostatic effect of a polarizable model environment was considered. The DeltaECCSD(T) - DeltaEMP2 corrections still remained close to their gas-phase values for four complexes with 0, +/-1 net charges. Good correlations (R2 = 0.918-0.958) for the in-environment MP2/aug-cc-pvtz and MP2/6-31+G* hydrogen-bonding energies facilitate the high-level prediction of these energies on the basis of relatively simple MP2/6-31+G* calculations.     

Density Functional Theory Study on Interaction between Catechin and Thymine

The interacting patterns and mechanism of the catechin and thymine have been investigated with the density functional theory Becke's three-parameter nonlocal exchange functional and the Lee, Yang, and Parr nonlocal correlation functional (B3LYP) method by 6-31+G*basis set. Thirteen stable structures for the catechin-thymine complexes have been found which form two hydrogen bonds at least. The vibrational frequencies are also studied at the same level to analyze these complexes. The results indicated that catechin interactedwith thymine by three different hydrogen bonds as N-H…O、C-H…O、O-H…O and the complexes are mainly stabilized by the hydrogen bonding interactions. Theories of atoms in molecules and natural bond orbital have been adopted to investigate the hydrogen bondsinvolved in all systems. The interaction energies of all complexes have been corrected for basis set superposition error, which are from -18.15 kJ/mol to -32.99 kJ/mol. The results showed that the hydrogen bonding contribute to the interaction energies dominantly. The corresponding bonds stretching motions in all complexes are red-shifted relative to that of the monomer, which is in agreement with experimental results.     

硝仿肼离子对相互作用的密度泛函理论研究

用密度泛函理论(DFT)方法,在B3LYP/6-31+G^**水平下,求得硝仿肼离子对体系势能面上2种全优化构型.经基组叠加误差(BSSE)和零点能校正,求得离子对最大相互作用能为-420.03kJ/mol,肼和硝仿离子化所需能量可由该值得到完全补偿.离子对间键的主要贡献为库仑作用,但键鞍点上的电子密度值表明共价作用也有显著的贡献.基于统计热力学求得相关体系的热力学性质,298.2K时由自由离子形成最稳定离子对的最大焓变和最大自由能变化分别为-419.72和-376.61kJ/mol     

An ab-initio study of the C3H6-HX, C2H4-HX and C2H2-HX hydrogen-bonded complexes with X=F or Cl.

MP2/6-31G** ab-initio molecular orbital calculations have been performed to obtain geometries, H-bond energies and vibrational properties of the C3H6-HX, C2H4-HX and C2H2-HX H-bonded complexes with X=F or Cl. The more pronounced effects on the structural parameters of the isolated molecules due to complexation are verified to the CC and HX bond lengths, which are directly involved in the H-bond formation. They are increased after complexation. The calculated H-bond lengths for the hydrogen complexes for X=F are shorter than those for x-Cl by about 0.55 A, whereas the corresponding experimental value is 0.58 A. The H-bond energies are essentially determined by the nature of the proton donor molecule. For X=F, the AE mean value is 20 kJ/mol, whereas it is approximately 14.5 kJ/mol for X-Cl. The H-bond energies including zero-point corrections show a good correlation with the H-bond lengths. The more pronounced effect on the normal modes of the isolated molecules after complexation occurs to the H-X stretching mode. The H-X stretching frequency is shifted downward, whereas its IR intensity is much enhanced upon H-bond formation. The new vibrational modes arising from complexation show several interesting features.     

Magnitude and directionality of interaction in ion pairs of ionic liquids: relationship with ionic conductivity

The intermolecular interaction energies of nine ion pairs of room temperature ionic liquids were studied by MP2/6-311G level ab initio calculations. The magnitude of the interaction energies of 1-ethyl-3-methylimidazolium (emim) complexes follows the trend CF(3)CO(2)(-) > BF(4)(-) > CF(3)SO(3)(-) > (CF(3)SO(2))(2)N(-) approximately PF(6)(-) (-89.8, -85.2, -82.6, -78.8, and -78.4 kcal/mol, respectively). The interaction energies of BF(4)(-) complexes with emim, ethylpyridinium (epy), N-ethyl-N,N,N-trimethylammonium ((C(2)H(5))(CH(3))(3)N), and N-ethyl-N-methylpyrrolidinium (empro) are not very different (-85.2, -82.8, -84.6, and -84.4 kcal/mol, respectively), while the size of the orientation dependence of the interaction energies follows the trend emim > epy approximately (C(2)H(5))(CH(3))(3)N > empro. Comparison with the experimental ionic conductivities shows that the magnitude and directionality of the interaction energy of the ion pairs play a crucial role in determining the ionic dissociation/association dynamics in the ionic liquids. The electrostatic interaction is the major source of attraction between ions. The induction contribution is small but not negligible. The hydrogen bonding with the C(2)-H of imidazolium is not essential for the attraction in the ion pair. The interaction energy of the BF(4)(-) complex with 1-ethyl-2,3-dimethylimidazolium (em2im) (-81.8 kcal/mol) is only 4% smaller than that of the emim complex.     

An ab initio study of intermolecular interactions of nitromethane dimer and nitromethane trimer

Different geometries of nitromethane dimer and nitromethane trimer have been fully optimized employing the density functional theory B3LYP method and the 6-31++G** basis set. Three-body interaction energy has been obtained with the ab initio supermolecular approach at the levels of MP2/6-31++G**//B3LYP/6-31++G** and MP2/aug-cc-pVDZ//B3LYP/6-31++G**. The internal rotation of methyl group induced by intermolecular interaction has been observed theoretically. For the optimized structures of nitromethane dimer, the strength of C--H...O--N H-bond ranges from -9.0 to -12.4 kJ mol(-1) at the MP2/aug-cc-pVDZ//B3LYP/6-31++G** level, and the B3LYP method underestimates the interaction strength compared with the MP2 method, while MP2/6-31++G**//B3LYP/6-31++G** calculated DeltaE(C) is within 2.5 kJ mol(-1) of the corresponding value at the MP4(SDTQ)/6-31G**//B3LYP/6-31++G** level. The analytic atom-atom intermolecular potential has been successfully regressed by using the MP2/6-31++G**//B3LYP/6-31++G** calculated interaction energies of nitromethane dimer. For the optimized structures of nitromethane trimer the three-body interaction energies occupy small percentage of corresponding total binding energies, but become important for the compressed nitromethane explosive. In addition, it has been discovered that the three-body interaction energy in the cyclic nitromethane trimer is more and more negative as intermolecular distances decrease from 2.2 to 1.7 A.     

BeH2与HX(X=F,Cl, Br,I)形成的二氢键复合物的结构特征与本质

对BeH2与HX(X=F, Cl, Br, I)形成的二氢键复合物的结构特征及本质进行了探讨. 在MP2/6-311++G(3d,3p)水平优化、频率验证, 得到复合物的分子结构, 用分子间距离及电子密度拓扑理论确认BeH2与卤化氢已形成了二氢键型复合物. 在MP2/6-311++G(3d, 3p)水平下进行基函数重叠误差(BSSE)校正后的结合能在-14.468 kJ·mol-1到-5.464 kJ·mol-1之间.用对称匹配微扰理论(SAPT)对复合物的结合能进行分解, 结果表明, BeH2…HX二氢键复合物中静电能对总吸引能的贡献都是最主要的, 但交换排斥能、诱导能、色散能对总结合能的贡献也很重要. 从BeH2…HF到BeH2…HI, 诱导能对总吸引能的贡献从37.8%逐渐减小到24.0%. 而色散能对总吸引能的贡献从BeH2…HF体系中的16.0%逐渐增加到BeH2…HI体系中的33.8%.     

Accurate interaction energies of hydrogen-bonded nucleic acid base pairs

Hydrogen-bonded nucleic acids base pairs substantially contribute to the structure and stability of nucleic acids. The study presents reference ab initio structures and interaction energies of selected base pairs with binding energies ranging from -5 to -47 kcal/mol. The molecular structures are obtained using the RI-MP2 (resolution of identity MP2) method with extended cc-pVTZ basis set of atomic orbitals. The RI-MP2 method provides results essentially identical with the standard MP2 method. The interaction energies are calculated using the Complete Basis Set (CBS) extrapolation at the RI-MP2 level. For some base pairs, Coupled-Cluster corrections with inclusion of noniterative triple contributions (CCSD(T)) are given. The calculations are compared with selected medium quality methods. The PW91 DFT functional with the 6-31G basis set matches well the RI-MP2/CBS absolute interaction energies and reproduces the relative values of base pairing energies with a maximum relative error of 2.6 kcal/mol when applied with Becke3LYP-optimized geometries. The Becke3LYP DFT functional underestimates the interaction energies by few kcal/mol with relative error of 2.2 kcal/mol. Very good performance of nonpolarizable Cornell et al. force field is confirmed and this indirectly supports the view that H-bonded base pairs are primarily stabilized by electrostatic interactions.