NBO输出结果分析

NBO 结果输出内容（1）2008-10-24 13:L POPULATIONS: Natural atomic orbital occupancies



For each of the 28 NAO functions, this table lists the atom to which the NAO is attached, the angular momentum type (s, px, etc.), the orbital type (whether core, valence, or Rydberg, with a conventional hydrogenic-type label), the orbital occupancy (number of electrons, or "natural population" of the orbital), and the orbital energy (in atomic units: 1 a.u. = 627.5 kcal/mol). Note that the occupancies of the Rydberg (Ryd) NAOs are typically much lower than tho of the core (Cor) and valence (Val) NAOs of the natural minimum basis (NMB) t, reflecting the dominant role of the NMB orbitals in describing molecular properties.



2. Summary of Natural Population Analysis:



This gment is an atomic summary showing the natural atomic charges (nuclear charge minus summed natural populations of NAOs on the atom) and total core, valence, and Rydberg populations on each atom:



3. Natural Population analesis



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Core 3.99900 ( 99.9749% of 4)



Valence 13.97712 ( 99.8366% of 14)



Natural Minimal Basis 17.97612 ( 99.8673% of 18)



Natural Rydberg Basis 0.02388 ( 0.1327% of 18)



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This reveals the high percentage contribution (typically, > 99%) of the NMB t to the molecular charge distribution.



4. Finally, the natural populations are summarized as an effective valence electron configuration ("natural electron configuration") for each atom:



Atom No Natural Electron Configuration



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C 1 [core] 2S( 1.08) 2p( 3.40)



N 2 [core] 2S( 1.43) 2p( 4.47)3p( 0.01)



H 3 1S( 0.77)



H 4 1S( 0.80)



H 5 1S( 0.77)



H 6 1S( 0.62)



H 7 1S( 0.62)



Although the occupancies of the atomic orbitals are non-integer in the molecular environment, the effective atomic configurations can be related to idealized atomic states in "promoted" configurations. For example, the carbon atom is en to have valence configuration (2s)1.09(2p)3.35, approximating the idealized promoted configuration for sp3 hybridization.



5. Natural Bond Orbital Analysis



This gments of the output summarize the results of NBO analysis. The first gment reports on details of the arch for an NBO natural Lewis structure:





Occupancies Lewis Structure Low High



Occ. ------------------- ----------------- occ occ



Cycle Thresh. Lewis Non-Lewis CR BD 3C LP (L) (NL) Dev



===================================================================

1(1) 1.90 17.94038 0.05962 2 6 0 1 0 0 0.02



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Structure accepted: No low occupancy Lewis orbitals



Normally, there is but one cycle of the NBO arch. The table summarizes a variety of information for each cycle:the occupancy threshold for a "good" pair in the NBO arch; the total populations of Lewis and non-Lewis NBOs;the number of core (CR), 2-center bond (BD), 3-center bond (3C), and lone pair (LP) NBOs in the natural Lewis structure; the number of low-occupancy Lewis (L) and high-occupancy (> 0.1e) non-Lewis (NL) orbitals; and the maximum deviation (Dev) of any formal bond order for the structure from a nominal estimate (NAO Wiberg bond index). The Lewis structure is accepted if all orbitals of the formal Lewis structure exceed the occupancy threshold (default = 1.90 electrons).



follows a more detailed breakdown of the Lewis and non-Lewis occupancies into core, valence, and Rydberg shell contributions:



This shows the general quality of the natural Lewis structure description in terms of the percentage of the total electron density (e.g., in the above ca, about 99.7%). The table also exhibits the relatively important role of the valence non-Lewis orbitals (i.e., the six valence antibonds, NBOs 23-28, listed below) relative to the extra-valence orbitals (the 13 Rydberg NBOs 10-22) in the slight departures from a localized Lewis structure model. The table also includes a warning about a carbon core orbital with slightly less than double occupancy.



7. Next follows the main listing of NBOs, displaying the form and occupancy of the complete t of orbitals that span the input AO space:



8. NHO Directional Analysis



NHO Directionality and "Bond Bending" (deviations from line of nuclear centers)



The "direction" of a hybrid is specified in terms of the polar (q) and azimuthal (f) angles (in the coordinate syst of the calling program) of the vector describing its p-component. For more general spldm hybrids the hybrid direction is determined numerically to correspond to the maximum angular amplitude. The hybrid direction is then compared with the direction of the line of centers between the two nuclei to determine the bending of the bond, expresd as the deviation angle (Dev, in degrees) between the two directions. For example, in the CH3NH2 ca shown above, the nitrogen NHO of the sCN bond (NBO 1) is bent away from the line of C-N centers by 3.0°, whereas the carbon NHO is approximately aligned with the C-N axis (within the 1.0° threshold for printing). The N-H bonds (NBOs 5, 6) are bent even further (by 4.4°). The information in this table is often uful in anticipating the direction of geometry changes resulting from geometry optimization (viz., likely reduced pyramidalization of the -NH2 group to relieve the ~4° nitrogen bond bending found in the tetrahedral Pople-Gordon geometry).



9. Perturba

tion Theory Energy Analysis



Second Order Perturbation Theory Analysis of Fock Matrix in NBO Basis



This analysis is carried out by examining all possible interactions between "filled" (donor) Lewis-type NBOs and "empty" (acceptor) non-Lewis NBOs, and estimating their energetic importance by 2nd-order perturbation the interactions lead to donation of occupancy from the localized NBOs of the idealized Lewis structure into the empty non-Lewis orbitals (and thus, to departures from the idealized Lewis structure description), they are referred to as "delocalization" corrections to the zeroth-order natural Lewis structure. For each donor NBO (i) and acceptor NBO (j), the stabilization energy E(2) associated with delocalization ("2e-stabilization") i ? j is estimated as









where qi is the donor orbital occupancy, ei, ej are diagonal elements (orbital energies) and F(i,j) is the off-diagonal NBO Fock matrix element. [In the example above, the nN ? sCH* interaction between the nitrogen lone pair (NBO9) and the antiperiplanar C1-H3 antibond (NBO 24) is en to give the strongest stabilization, 8.13 kcal/mol; this interaction is displayed from all angles on the NBO homepage.] As the heading indicates, entries are included in this table only when the interaction energy exceeds a default threshold of 0.5 kcal/mol.



10. Natural Bond Orbitals (Summary)



Next appears a condend summary of the principal NBOs, showing the occupancy, orbital energy, and the qualitative pattern of delocalization interactions associated with each:



This table allows one to quickly identify the principal delocalizing acceptor orbitals associated with each donor NBO, and their topological relationship to this NBO, i.e., whether attached to the same atom (geminal, "g"), to an adjacent bonded atom (vicinal, "v"), or to a more remote ("r") site. The acceptor NBOs will generally correspond to the principal "delocalization tails" of the natural localized molecular orbital (NLMO) associated with the parent donor NBO. [For example, in the table above, the nitrogen lone pair (NBO 9) is en to be the lowest-occupancy



(1.978 electrons) and highest-energy (-0.446 a.u.) Lewis NBO, and to be primarily delocalized into antibonds 24, 25, 26 (the vicinal sCH NBOs). The summary at the bottom of the table shows that the Lewis NBOs 1-9 describe about 99.7% of the total electron density, with the remaining non-Lewis density found primarily in the valence-shell antibonds (particularly, NBO 24).]









自然键轨道输出格式说明：



轨道类型 BD ： 成键轨道 CR：内层轨道 LP ：孤对电子 RY：Rydberg弥散轨道 BD* :反键轨道