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New NBO 6.0 Features

  • Improved "Link-Free" Connectivity to Many New Host Programs
    NBO 6 introduces a fundamentally new (link-free!) interactive connectivity to electronic structure system (ESS) codes, based on standard message-passing protocols made available as freeware to all cooperating ESS vendors. Highly interactive ESS/NBO applications that were previously restricted to Gaussian and GAMESS host programs can now be carried out with a broad range of alternative ESS hosts.

  • Generalized Output and Labelling for Ground and Excited Species
    NBO 6 is now properly generalized and reformatted for arbitrary electronic excitations and spin multiplicities, including the localized Lewis-like and resonance patterns of excited states.
"Rydberg bond" and hybrids in 3T4 CH3CHO

  • Natural Cluster Unit (NCU) Analysis
    NBO 6 now identifies the specific clustering patterns (emergent "building blocks") that are associated with specific ranges of interatomic interaction strength, allowing one to isolate the distinguishing donor-acceptor interactions over the entire range of metallic, molecular, and supramolecular aggregation phenomena.
Li9 at τNCU = 0.350: (Li5)-0.447(Li+0.111)4

  • Natural Coulomb Electrostatics (NCE) Analysis
    NBO 6 now provides NPA-based evaluation of Lewis and non-Lewis contributions to apparent Coulomb potential energy, providing an estimate of classical-like "electrostatic" effects to complement evaluation of steric and resonance-type donor-acceptor contributions to intra- and intermolecular interactions.
NCE atomic charges (L/NL) in (H2O)2

  • Natural Bond Critical Point (NBCP) Analysis
    NBO 6 now provides comprehensive NBO-based analysis of topological "bond critical point" (BCP) properties, as characterized by the QTAIM theory of Bader and coworkers. Atomic charges and other "basin" properties of QTAIM-type "atoms in molecules" can thereby be quantitatively compared and contrasted with corresponding properties of NAO-based "natural atoms in molecules" (NAIM), providing alternative interpretations of many QTAIM-based topological descriptors.
QTAIM (dashed) vs. NAIM (solid) partitioning of CN bond density in methylamine

  • Extended Multi-Center NBO Search
    NBO 6 now conducts automated searches for both hypovalent 3c/2e (3CBOND search) and hypervalent 3c/4e bond motifs (3CHB search), obviating the former need for user intervention.
3c/2e sigma-bond in cyclobutenyl cation

  • Local NRT Analysis
    NBO 6 now allows NRT analysis to be restricted to local subregions (specified by input bracket-list of "active" atoms), thereby allowing resonance features of much larger polyaromatic and metallic systems to be analyzed by "divide and conquer" strategy. Many other algorithmic improvements make NRT searches more robust, reliable and efficient than in previous versions.
Local and full NRT bond orders for C6H5ICl2

  • High-Order Multiple Bonding
    NBO 6 now makes general provision for $CHOOSE structures incorporating high-order metal-metal bond orders (up to hextuple bonds!), consistent with predicted (and observed) bonding patterns in dinuclear and polynuclear species.
"Beyond-σ" metal-metal bonds in HWWH

  • CML Support for NRT Resonance Structures
    NBO 6 now includes "NRTCML" and other keywords to generate Chemical Markup Language (.cml) or other graphical-format input to display NRT resonance structures in common structural viewers such as ChemDraw and MarvinView.
NRTCML diagrams for leading resonance structures of C6H5ICl2

  • General 1e Property (PROP) Analysis
    NBO 6 now extends NBO analysis to any 1-electron property for which matrix elements are available from the host program. This allows DIPOLE-style analysis to be extended to spin-density, kinetic energy, nuclear-electron potential energy, and many other properties of chemical interest.

  • Generalized operator and transformation matrix (MATRIX) keywords
    NBO 6 now provides enhanced (and simplified!) keyword tools to display operator matrices for any available 1-e operator in any desired basis or transformation matrices that explicitly relate any chosen pair of basis sets to one another.

  • Complete Line of PC-Windows, MacOSX, and Linux/Unix Binary Options for Interactive or Stand-Alone Usage
    NBO 6 is now available in fully functional binary .exe implementations for PC-Windows XP/V/W7 or MacOSX10 systems, in addition to common Linux/Unix configurations. For stand-alone GenNBO6 usage, just include the "ARCHIVE" keyword in a standard NBO-linked electronic structure job (including those from earlier NBO versions) to obtain the .47 input file and run alternative analyses (without recomputing the wavefunction) from the convenience of the PC/Mac/Linux desktop. Alternatively, add binary NBO6 to the environment of your NBO6-compatible host ESS and watch the ESS/NBO6 binary pair "come to life" to cooperatively tackle complex interactive tasks that previously required linking.

With exceptions as noted above, NBO 6.0 is designed to be compatible with earlier NBO 3/4/5-level versions as nearly as possible. Experienced NBO users will find that familiar options run practically unchanged, with smooth and intuitive migration to newer keywords, features, and output format.


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