"It is nice to know that the computer understands the problem, but I would like to understand it too." - Eugene Wigner

The Natural Bond Orbital (NBO) program NBO 6.0 is a discovery tool for chemical insights from complex wavefunctions. NBO 6.0 is the current version of the broad suite of 'natural' algorithms for optimally expressing numerical solutions of Schrödinger's wave equation in the chemically intuitive language of Lewis-like bonding patterns and associated resonance-type 'donor-acceptor' interactions.

Through their close association with elementary Lewis structure diagrams, NBOs provide a direct link to familiar valency and bonding concepts. Unlike delocalized MOs (whose sprawling forms vary bewilderingly even between closely related systems), NBOs are highly conserved and transferable from one molecular environment to another.

NBOs are intrinsic realizations of orbital-type bonding concepts as originally envisioned by Pauling, Mulliken, and Coulson. Unlike methods based on derivatives of charge density (a quasi-classical concept), NBO analysis exhibits the unifying beauty of quantum phase-matching and superposition principles in all chemical phenomena.

NBO provides mutually consistent and comprehensive analysis tools, ensuring harmonious chemical interpretations from one property to another. The program is uniformly implemented in leading electronic structure packages, providing an authoritative framework for state-of-the-art professional discourse. Widespread acceptance of the NBO paradigm is reflected in the burgeoning number of published applications (currently, ~1500 per year).

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What Are NBOs?

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What's New in NBO 6?

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August 24, 2015: Organometallics cover "illustrates the dilemma created by applications of different methods, here NBO and EDA-NOCV, for the extraction of bonding information from ab initio computations - which method is better? Because the analyses represent different interpretations, rather than observables, there is no bottom-line criterion for such a judgment. We are reminded of the complementary contrariness of Tweedledee and Tweedledum in Lewis Carroll's Through the Looking Glass and their inability to provide Alice with directions on the best way out of the woods. The cover was conceived by Russ Hughes, and the artwork was created by Kate Nikles." [C. R. Landis, R. P. Hughes, and F. Weinhold, "Bonding Analysis of TM(cAAC)2 (TM = Cu, Ag, and Au) and the Importance of Reference State," Organometall. 34, 3442-3449 (2015)]

   January 15, 2015: In recognition of the 2nd anniversary of NBO 6.0 release, the legacy NBO 5.9 program and website is being decommissioned from active maintenance and support. Users requiring NBO 5.9 for compatibility with NBO6-incompatible or other older ESS versions may still order through the legacy NBO5 order form.

   September 22, 2014: C&E News cover story "Pushing the Limits of Chemical Bonding" features NBO-based characterization of anti-electrostatic H-bonding and other challenging cluster interactions.

   June 1, 2014: New ORCA v. 3.0.2 release now provides improved (correlated) densities for NBO6-level analysis of DLPNO-CCSD(T) and other advanced methods (more...)

   May 14, 2014: Q-Chem, Inc. announces release of Q-Chem v. 4.2 with NBO6 interface included (more...)

   October 1, 2013: The Frank Neese group of MPI-Mülheim announces release of NBO6-compatible Orca v. 3.0 (more...)

   August 16, 2013: Schrödinger Inc. announces release 2013-2 of Jaguar v. 8.1, with NBO6 included (more...)

  July 28, 2013: NBO6-level NBOPro v.6 now available (more...).

  July 27, 2013: Marcel Patek announces a set of utilities to assist $NBO input preparation ("Gennbo Helper") and Jmol-based orbital visualizations ("Jmol-NBO Visualization Helper") in NBO-based applications. Companion videos provide useful tutorial introduction to these utilities (more...)

May 8, 2013: J. Comp. Chem. cover feature: "NBO 6.0, the next generation in natural bond orbital methods,... includes link-free connectivity for interfaces to popular electronic structure programs, new methods of analysis, and numerous algorithmic enhancements. The cover image is made with the NBOView 2.0 program and shows the sigma-type, 3-center/2-electron bonding NBO of the cyclobutenyl cation that arises from the strong overlap of the vacant valence orbital at C1 with the C2-C3 bond. Automated multicenter bond searches are one of the many new features of the NBO program." [JCC 34, 1472 (2013)]

   May 6, 2013: NBO6-compatible Gaussian 09 Rev. D.01 now available, with "pop=npa6", "pop=nbo6read", and related keywords (more...)

   April 11, 2013: NBO6-compatible Molpro v. 2012.1 now available (more...)

   April 8, 2013: SCM announces release of ADF2013, with NBO6 included (more...)

   March 12, 2013: "Early View" of J. Comp. Chem. article "NBO 6.0: Natural Bond Orbital Analysis Program" (DOI: 10.1002/jcc.23266) now available (more...)

   February 4, 2013: NBO6 binaries for PC-Windows now available (more...)

   JANUARY 20, 2013: NBO6 ANNOUNCEMENT DAY (more...)

   December, 2012: GAMESS releases NBO6-compatible source code version (more...)

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