Efficient diffuse function‐augmented basis sets for anion calculations. III. The 3‐21+G basis set for first‐row elements, Li–F

Clark, Timothy; Chandrasekhar, Jayaraman; Spitznagel, Günther W.; Schleyer, Paul von Ragué

doi:10.1002/jcc.540040303

Cited by 6,522 publications

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“…hydrogen, boron, carbon, and nitrogen the 6-311 ++ G** basis [32][33][34] was used, and for the aluminum, phosphorus, sulfur, and silicon the 6-311G** 35,33 basis was used. We refer to this combination as basis1.…”

Section: B Inorganic Chemistrymentioning

confidence: 99%

The Electronic Structure of Inorganic Benzenes: Valence Bond and Ring-Current Descriptions

et al. 2005

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Valence bond (VB) theory and ring-current maps have been used to study the electronic structure of inorganic benzene analogues X 6 H 6 (X ) C (1), Si (2)), X 6 (X ) N (3), P (4)), X 3 Y 3 H 6 (X,Y ) B,N (5), B,P (6), Al,N (7), Al,P (8)), and B 3 Y 3 H 3 (Y ) O ( 9), S ( 10)). It is shown that the homonuclear compounds possess benzene-like character, with resonance between two Kekule ´-like structures and induced diatropic ring currents. Heteronuclear compounds typically show localization of the lone pairs on the electronegative atoms; Kekule ´-like structures do not contribute. Of the heteronuclear compounds, only B 3 P 3 H 6 (6) has some benzene-like features with a significant contribution of two Kekule ´-like structures to its VB wave function, an appreciable resonance energy, and a discernible diatropic ring current in planar geometry. However, relaxation of 6 to the optimal nonplanar chair conformation is accompanied by the onset of localization of the ring current.

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Section: B Inorganic Chemistrymentioning

confidence: 99%

The Electronic Structure of Inorganic Benzenes: Valence Bond and Ring-Current Descriptions

et al. 2005

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“…All DFT calculations were performed on the Gaussian03 quantum chemical program [68] with the unrestricted (U) B3LYP functional [69,70] and a Gaussian-type double-6-31ϩϩG(d,p) basis set [71,72]. Minima and transition structures were characterized as such by means of harmonic frequency calculations.…”

Section: Computational Detailsmentioning

confidence: 99%

Kinetics for tautomerizations and dissociations of triglycine radical cations

Siu

Zhao

Laskin

et al. 2009

J. Am. Soc. Mass Spectrom.

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[7,8], infrared multiphoton dissociation (IRMPD) [9], and blackbody radiation [10]. The mechanisms by which protonated peptides dissociate have, therefore, generated much interest [11,12]. Charge-driven amide bond cleavages are induced by the mobile proton, giving b-or y-type ions, which are, respectively, the N-or C-terminal fragments [1,2]. By contrast, open-shell peptide radical cations produced in electron-capture [13][14][15] or electron-transfer dissociation experiments [16] give c-or z-type ions, by cleaving the N-C ␣ bond adjacent to the aminoketyl radical being formed [17][18][19][20]. The substantial fragmentation differences between protonated and radical cationic peptide provide useful complementary peptide sequencing information [21][22][23]. Ultraviolet (UV) photodissociation has also been employed for peptide fragmentation [24]. UV photodissociation of a peptide/protein chemically modified to incorporate an appropriate chromophore can generate a radical cation that undergoes site-specific, radical-driven dissociations, which are useful in protein identifications [25,26]. Peptide radical cations have also been generated via low-energy CID of a ternary metal complex containing the peptide and auxiliary ligands [27][28][29][30][31][32][33][34][35][36][37]. These methodologies open new avenues whereby the fragmentation chemistries of peptide radical cations can be examined and exploited.Dissociation at an amino-acid side chain is commonplace in the CID of peptide radical cations. These fragmentations are useful in providing differentiating signatures for isobaric residues present [14, 29, 38 -40], e.g., between leucine and isoleucine [14,29], and between aspartic acid and isoaspartic acid [38,39]. For aromatic amino acid residues, cleavage of the C ␣ -C ␤ bond eliminates pquinomethide from tyrosine and 3-methylene indolenine from tryptophan, yielding a glycyl radical with the unpaired electron located on the ␣-carbon [12,27,28,30]. Such ␣-centered radicals have been identified in some anaerobic enzymes [41][42][43] [50]. A radical transfer from the thiyl group in the cysteine residue to a neighboring glycine residue by ␣-hydrogen-atom abstraction generates an ␣-centered radical [51,52], which is stabilized by -electron delocalization between the adjacent electron-withdrawing carbonyl group and the electron-donating amide nitrogen. This stabilization is known as the captodative effect [53]. The intrinsic stability of an amino-acid captodative radical has recently been verified by IRMPD spectroscopy on the histidine radical cation in the Address reprint requests to Professor K

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“…In the whole study presented in this work, only Pople's split-valence basis sets [82][83][84][85][86][87][88][89] have been investigated. Among the many reasons behind this choice, we would like to mention the following ones:…”

Section: Basis Set Selectionmentioning

confidence: 99%

“…For consistence, the diffuse and polarization functions used for 3-21G and 4-31G are the same as the ones for 6-31G and 6-311G [84,85,88,89].…”

Section: Basis Set Selectionmentioning

confidence: 99%

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Efficient model chemistries for peptides. I. General framework and a study of the heterolevel approximation in RHF and MP2 with Pople split‐valence basis sets

Echenique

Alonso

2008

J Comput Chem

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We present an exhaustive study of more than 250 ab initio potential energy surfaces (PESs) of the model dipeptide HCO-L-Ala-NH2. The model chemistries (MCs) used are constructed as homo-and heterolevels involving possibly different RHF and MP2 calculations for the geometry and the energy. The basis sets used belong to a sample of 39 selected representants from Pople's split-valence families, ranging from the small 3-21G to the large 6-311++G(2df,2pd). The reference PES to which the rest are compared is the MP2/6-311++G(2df,2pd) homolevel, which, as far as we are aware, is the more accurate PES of a dipeptide in the literature. The aim of the study presented is twofold: On the one hand, the evaluation of the influence of polarization and diffuse functions in the basis set, distinguishing between those placed at 1st-row atoms and those placed at hydrogens, as well as the effect of different contraction and valence splitting schemes. On the other hand, the investigation of the heterolevel assumption, which is defined here to be that which states that heterolevel MCs are more efficient than homolevel MCs. The heterolevel approximation is very commonly used in the literature, but it is seldom checked. As far as we know, the only tests for peptides or related systems, have been performed using a small number of conformers, and this is the first time that this potentially very economical approximation is tested in full PESs. In order to achieve these goals, all data sets have been compared and analyzed in a way which captures the nearness concept in the space of MCs. * Corresponding author. E-mail address: pnique@unizar.es 1The most important results of the study are the following: First, that the convergence in method is not achieved in the RHF → MP2 step. Second that the transferability of basis set accuracy from RHF to MP2 is imperfect. These two conclusions lead us to discourage the use of RHF MCs for peptides. Regarding the relative efficiency of the Pople's basis sets, we recommend the inclusion of polarization functions in 1st-row atoms and we discourage the use of basis sets containing doubly-split polarization shells and no diffuse functions. Also, we have found that 6-31G(d) is very efficient for calculating the geometry, and that both the RHF and MP2 infinite basis set limits are approximately reached at 6-311++G(2df,2pd). Finally, related to the heterolevel approximation, we conclude that it is essentially correct for the description of the conformational behaviour of HCO-L-Ala-NH2 both at RHF and MP2. Nevertheless, we place a cautionary remark on the use of RHF geometries with MP2 single-points: Whereas this practice could be accurate enough for short peptides, the accumulation of errors may render it unreliable for longer chains and require the use of MP2 geometries.

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Efficient diffuse function‐augmented basis sets for anion calculations. III. The 3‐21+G basis set for first‐row elements, Li–F

Abstract: The relatively small diffuse function‐augmented basis set, 3‐21+G, is shown to describe anion geometries and proton affinities adequately. The diffuse sp orbital exponents are recommended for general use to augment larger basis sets.

Cited by 6,522 publications

References 28 publications

The Electronic Structure of Inorganic Benzenes: Valence Bond and Ring-Current Descriptions

The Electronic Structure of Inorganic Benzenes: Valence Bond and Ring-Current Descriptions

Kinetics for tautomerizations and dissociations of triglycine radical cations

Efficient model chemistries for peptides. I. General framework and a study of the heterolevel approximation in RHF and MP2 with Pople split‐valence basis sets

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