"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
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
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
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).
NBO 7.0 is here!
As of 12pm CST, November 15, 2018, the NBO 6.0 program
and this website have reverted to LEGACY status and will no longer
be actively maintained. Please navigate to
the NBO7 website
for current NBO7-level products.
[Check here for latest bugfix
and update announcements]
March 12, 2018:
The NBO team is pleased to announce release
of NBO 6.0.18, a fully functional
NBO6 interface for newly released G16 Rev. B.01.
The NBO 6.0.18 release is also compatible
with earlier G16 Rev. A.03 and is now
available for download by new purchasers
and current NBO6 license holders.
March 9, 2018: Legacy 32-bit NBO 6.0 Linux x86
Because legacy x86_32 hardware is no longer available to the
NBO development team, distribution packages for
NBO 6.0 Linux x86 can no longer be updated
for minor revisions and bugfixes. Until further
notice, the NBO 6.0 Linux x86 software products
(individual or site license) will remain available
on the website order form. Current NBO 6.0
Linux x86 license holders may contact
TCINBO@CHEM.WISC.EDU (with original purchase
information) to have their license converted
to the corresponding NBO 6.0 Linux x86_64 product
at no additional cost.
March 14, 2017:
A new, partially G16-enabled interim NBO6 distribution --
NBO 6.0.15, dated 14-Mar-2017) -- is now available for download.
(However, NBO 6.0 binaries are no longer being updated for
legacy x86_32 platforms, which are increasingly passing
out of service.) The new distribution remains fully compatible with
G09 Revs. D, E, but is only partially compatible with G16, Rev. A,
due to significant $DEL and DENSITY issues described below:
(i) NBO $DEL options are severely restricted. For the
time being, closed-shell NBO deletions require a non-standard route
(as described in installation instructions) and open-shell
deletions don't work at all.
(ii) Correlated MP2 or CI densities cannot be
The Gaussian "density=current" keyword is not correctly
implemented, so that only the SCF density (rather than the
properly correlated MP2 or CI density) is provided to the
NBO program for analysis.
It is expected that these remaining G16-incompatbilities
will all be fixed when the first minor update to G16 is
released, most likely in May 2017. Devoted G09/NBO6 users
may wish to defer upgrades from G09 to G16 until this first
minor update to G16 is released by Gaussian Inc..
The 14-Mar-2017 distribution
includes a number of other features of interest
to general NBO users,
whether or not an upgrade to G16 is contemplated:
It is recommended that all current NBO 6.0 license holders
(except 32-bit linux users) consider updating to this version.
- Dynamic memory allocation is now supported, allowing one
to exceed the former 2Gb address space of 32-bit applications (see NBO
Program Manual, p. B-6).
- The default NAO search algorithm has been modified to better
preserve core-valence separation in rare cases
where numerical near-degeneracies can lead to unphysical core-valence
mixing. The numerical effects are generally negligible except
where they become necessary. The "OLDNAO" keyword restores the
legacy NAO algorithm for comparison purposes.
- A formatting limit in PLOT (.31) filies has been revised to
allow applications to larger molecules.
- Linux x86 binaries for NBO 6.0 were formerly
prepared with Ubuntu 12, which is nearing "end of service"
status. Present linux binaries are now prepared with Ubuntu 16,
which no longer supports 32-bit x86 applications. Users requiring 32-bit
linux applicability should order source code NBO 6.0
that can be compiled for the platform of interest.
January 23, 2017: Gaussian 16 Compatibility with NBO6?
Recent release of Gaussian 16 presents significant
with current NBO 6.0. Due to changes in the G16 matrix element
file and erroneous standard route for POP=NBO6Del options
(only reparable in some future G16 revision)
significant code-patches may be required to achieve even
partial compatibility with G16, while also preserving
full interactive compatibility with G09 Revs. D, E.
We intend to announce a new NBO 6.0 distribution
in the near future that allows an interim level of
G16/NBO6 interfacing and includes possible work-arounds
for some known incompatibilities. In the usual manner,
current NBO 6.0 license holders
may use their original download code to obtain the patched
code from the NBO repository and explore the possibilities
of interim G16/NBO6 interfacing for their applications
of interest. Keep watching this space for an announcement
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.
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
May 14, 2014: Q-Chem, Inc.
announces release of Q-Chem v. 4.2 with NBO6 interface included
October 1, 2013: The Frank Neese group of MPI-Mülheim
announces release of NBO6-compatible Orca v. 3.0
August 16, 2013: Schrödinger Inc. announces release 2013-2 of
Jaguar v. 8.1, with NBO6 included
July 28, 2013:
NBOPro v.6 now available
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
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",
and related keywords
April 11, 2013: NBO6-compatible Molpro v. 2012.1 now available
April 8, 2013: SCM announces release of ADF2013, with NBO6 included
February 4, 2013: NBO6 binaries for PC-Windows now available
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
JANUARY 20, 2013: NBO6 ANNOUNCEMENT DAY
December, 2012: GAMESS releases NBO6-compatible
source code version (more...)