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

NBO Intro Slideshow

What Are NBOs?

NBO Keywords/Output

NBO Tutorials

What's New in NBO 7?

The Natural Bond Orbital (NBO) program NBO 7.0 is a discovery tool for chemical insights from complex wavefunctions. NBO 7.0 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 the delocalized MOs (whose sprawling forms vary bewilderingly even between closely related systems) or unitarily-equivalent LMOs (whose occupancy degeneracies persist for any preferred "localizing" criterion), the NBOs have unique occupancies and spatial forms that are highly conserved and transferable from one molecular environment to another.

NBOs are local eigen-properties of the input wavefunction, the 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, ca. 2000 per year).

News Archive FAQ Featured apps NBO team contact us

[Check here for latest bugfix and update announcements]

February 8, 2021:

New release NBO 7.0.10 (8-Feb-2021) is now available for download by all licensed users. This release includes a parallel implementation of NRT for Linux and MacOS (see the PARALLEL.NRT file in the nbo7 root directory for details) and bug fixes for gfortran 6-10. By default, the NRT algorithm now cycles to convergence (NRTCYC=0) and eliminates resonance forms that do not contribute to the resonance hybrid for six consecutive cycles (NRTCULL=6).

May 21, 2020:

New release NBO 7.0.9 (21-May-2020) is now available for download by all licensed NBO7 and NBOPro7@Jmol users. The update includes fixes for NLMO and RNBO analyses, Th point-group symmetry, new NRTPR keyword, and new NBOMEM environment variable for dynamic memory allocation for GenNBO G09NBO and G16NBO interface programs (making source-code edits largely unnecessary for large systems that exceed default memory limits of the compiled binary program).

February 21, 2020:

The e-order form for NBO 7.0 products has been revised to include a link to the current License Agreement. In addition, the ordering process for a Site License now requires identification and title of the institutional officer with appropriate signatory authority, as well as the "Responsible Individual" (if different from the "Authorized Company or Institutional Signatory") who directly receives the downloaded program and administers its usage on site resources.

February 17, 2020:

The e-order form for products from the former NBO 6.0 website (decommissioned in November 2018) is being de-activated as of today. However, the NBO6 download repository will remain accessible to licensed users until March 1, 2020, after which all services to pre-NBO7 products will cease.

February 11, 2020:

New release NBO 7.0.8 (11-Feb-2020) is now available for download by all licensed NBO7 and NBOPro7@Jmol users.

November 4, 2019:

The online NBOrXiv (.47 file repository) for RUN applications in NBOPro7@Jmol has been restored (after the security-mandated URL change that broke communications in August). Thanks to Zhi Yuan Foo for assistance, and apologies to users who were affected by temporary NBOrXiv inaccessibility.

September 9, 2019:

New release NBO 7.0.7 (now available for download by all licensed NBO7 users) corrects a problem in the initial G16 Rev. C.01 implementation of NEDA (PC-windows G16W/NBO7 only) and introduces the new NRTLONG keyword, which initiates a more thorough NRT search for 3c/4e long-bonding structures (all OS options).

July 24, 2019:

NEDA for Gaussian (G16 Rev. C.01 or later): Recently released G16 Rev. C.01 includes improved interactive functionality with NBO 7.0.5, including a new full-featured implementation of Natural Energy Decomposition Analysis (NEDA) that is now available for download by all licensed NBO7 users.

July 14-19, 2019: Bremen, Germany

"Tools for Chemical Bonding" Workshop, sponsored by the European Crystallographic Association and hosted by Prof. Simon Grabowsky of the University of Bremen, will feature NBO developers Clark Landis and Eric Glendening in a presentation of "Discovering Chemistry with NBO7" on Monday, July 15.

June 7, 2019:

NBO7: New Vistas in Localized and Delocalized Chemical Bonding: Journal article (DOI: 10.1002/JCC.25873) describing new and improved features of NBO 7.0 is now available on the Journal of Computational Chemistry website.

January 2, 2019:

New release NBO 7.0.2 that cures the PC-Windows issue of 11/19/2018 is now available for download by all licensed NBO7 and NBOPro7@Jmol users.

December 18, 2018:

Early Download Problem for NBOPro7@Jmol: In the initial download package for NBOPro7@Jmol, the .zip file failed to include the "unix2dos" utility that is needed for RUN, VIEW, and SEARCH modules. All NBOPro7@Jmol license holders should obtain a fresh download package with the download code provided at time of purchase. Our apologies!

December 5, 2018:

Early Download Problems: In early NBO7 purchases, the email sent to license holders contained the wrong link (the legacy NBO6 download link). The correct link address for NBO7 downloads should end in "nbo7.cgi" (not "nbo6.cgi"). Our apologies!

November 20, 2018:

If you purchased NBO 6.0 in the last few weeks before NBO 7.0 release (specifically, in the period October 15-November 15, 2018), you are eligible for a 50% refund on the purchase price for immediate upgrade to current NBO 7.0 (offer expires December 15, 2018). Contact Cara Jenkins (tcinbo@chem.wisc.edu) with your NBO7 license information to request the refund.

November 19, 2018:

Temporarily, NBO 7.0 for PC-Windows is being released only in 32-bit binaries without functioning MEMORY keyword for dynamic memory allocation. (The default scratch memory is still 1Gb, equivalent to that of the intended 64-bit implementation.) Watch here for notification when the full-featured 64-bit NBO 7.0 binary for PC-Windows (equivalent to linux and MacOSX binaries) replaces the temporary 32-bit version in the website distribution link, at which time licensed purchasers of NBO 7.0 (PC-Windows) can download the 64-bit program at their convenience.

November 15, 2018: NBO7 ANNOUNCEMENT DAY

NBO 7.0 is announced!

Following years of program development and cooperation with affiliated ESS providers, leading members of the NBO Team (Eric Glendening, Clark Landis, Frank Weinhold) unveiled the new nbo7.chem.wisc.edu website and announced public availability of the NBO 7.0 program, as well as enhanced NBOPro7@Jmol program.

Claisen rearrangement illustrated with Resonance NBOs (RNBOs),
the newest addition to the NBO-based orbital family

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