"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 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 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 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, >2000 per year).

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Quick Slideshow Intro to NBO & NBOView

What Are NBOs?

NBO Keywords & Sample Output

NBO Tutorials

What's New in NBO 7?

[Check here for latest bugfix and update announcements]

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, Frank Weinhold, Clark Landis) unveiled the new nbo7.chem.wisc.edu website and announced public availability of the NBO 7.0 program, as well as enhanced NBOPro@Jmol program.

Claisen rearrangement illustrated with Resonance NBOs (RNBOs),
newest addition to the NBO-based orbital family
NBO 6 Logo NBO 6 Logo NBO 6 Logo

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 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.
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!

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