One cannot understand ... the universality of the laws of nature, the relationship of things, without an understanding of mathematics. There is no other way to do it." - Richard Feynman

The NBO 5.0 website and associated order form (for NBO5-level versions that link with older ESS versions) has been removed from service (October 2017).

Still older legacy code (such as the 1980s-vintage "NBO 3.1" included in current Gaussian distributions) is not supported by the NBO development team and is not considered to be of publishable reliability except for routine organic applications in modest basis sets. Users encountering difficulties with legacy NBO code should contact the help desk of the host ESS that provides such code.

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NBO Product Offerings

NBO 6.0 General Natural Bond Orbital Analysis program, for stand-alone GenNBO usage with any valid NBO archive .47 file, as well as for cooperative ESS/NBO interactions with any "NBO6-compatible" host electronic structure system (ESS). [Available as a binary executable (.exe) program for linux/mac/unix or PC-Windows platforms, or in source fortran code for compilation/linking on other platforms.]

Firefly NBO password Required password to activate NBO options in the Firefly (PC-GAMESS) program.

NBOView 2.0 NBO orbital viewer, to display profile (1D), contour (2D), and rendered surface plots (3D) of localized (NAO, NHO, NBO), semi-localized (NLMO), and delocalized (MO) orbitals (or pre-orthogonal counterparts). NBOView 2.0 features increased storage and full dimensional (basis/atoms) and angular (s/p/d/f/g) compatibility with NBO 6.0. [Available only as a binary executable (.exe) for PC-Windows.]

NBOPro 6.0 All-inclusive NBO6-level utility program for I/O-free integrated management of computational projects from initial molecular model to final chemical descriptors. NBOPro is composed of four interacting program modules:
  (1) NBOModel molecular design editor;
  (2) NBORun (GenNBO6-level) analysis;
  (3) NBOView 2.0 orbital viewer;
  (4) NBOSearch (NBO6-level) interactive data miner.
[Full GenNBO6 and NBOView 2.0 capability included; available only as a binary executable (.exe) for PC-Windows systems. Note that this program may not display properly on PCs with installed Windows-CJK (Chinese-Japanese-Korean) operating system and character sets; see FAQ 31.]

(The previous NBO5-level NBOPro v. 1.0 program has been moved to the NBO5 website order form. Upon request to, previous purchasers of the legacy NBO5-level program may upgrade to current NBOPro 6.0 at no cost.)

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