New in Spartan'18 Parallel Suite:
Set Torsions. A new algorithm has been implemented (a significant improvement over previous routines) for molecules that have both rings with >6 members and rotatable bonds (many if not most natural products fit this category). It is perhaps an order of magnitude faster previous versions.
Equilibrium Conformer. Now includes a quantum mechanics entry which leads to a selection of (two) multi-step procedures. Returned is the lowest-energy conformer according to the method used in the last step of the procedure (either B3LYP/6-311+G(2df,2p)[6-311+G*] or ωB97X-V/6-311+G(2df,2p)[6-311+G*]). A wide variety of user-defined procedures are also available.
Conformer Distribution. Like the Equilibrium Conformer task, this also now includes a quantum mechanics entry which leads to a selection of (two) multi-step procedures (as well as a wide variety of user-defined procedures. The lowest-energy conformer is returned (according to the method used in the last step of the method chosen, either B3LYP/6-311+G(2df,2p)[6-311+G*] or ωB97X-V/6-311+G(2df,2p)[6-311+G*]. The energy, dipole moment, and charges correspond to a proper Boltzmann weighted average. A supplementary list of the individual conformers (and their Boltzmann weights) is provided.
Boltzmann Averaged NMR. A new computational task which utilizes the same automated multi-step procedures as Conformer Distribution. The NMR step involves either B3LYP/6-31G* or ωB97X-D/6-31G*. The Boltzmann weights are obtained from B3LYP/6-311+G(2df,2p)[6-311+G*] or ωB97X-V/6-311+G(2df,2p)[6-311+G*]), respectively.
While there are only two computational model options for NMR, alternative procedures may be used to obtain the Boltzmann weights (as in Conformer Distribution). Returned are Boltzmann averaged chemical shifts (and coupling constants if requested). A supplementary list of the individual conformers (and their Boltzmann weights) is provided. This is meant for conformationally-flexible molecules but also functions where there is only one conformer. The NMR check-box (and a new Coupling Constant check-box) are available as a Compute: option when either Energy or Equilibrium Geometry tasks are specified.
DP4 Support. The DP4 measure proposed by Goodman may be applied to find the best match either assuming the conformer provided for each (stereo/regio) isomer or Boltzmann averaging of conformers for each isomers. Both are automatic (starting from a list of one conformer for each isomer) and both may be based on either the B3LYP/6-31G* or ωB97X-D/6-31G* models for chemical shift calculation.
Coupling Constants. Spartan previously employed a Karplus-type approach to estimate 3-bond HH coupling constants (what the textbooks talk about when they draw proton spectra). This has been extended to 2-bond HH coupling constants. 2, 3 and 4-bond (and higher) CH coupling constants which are “almost never” reported as numbers but are essential to the construction of 2D HMBC spectra cannot be obtained empirically. This latest release includes an efficient procedure (involving only the so-called Fermi contact term and using the so-called PCJ-0 basis set) which provides satisfactory results. Spartan can utilize additional terms and use larger basis sets, but neither approach leads to statistically significant improvements. The CH calculations also lead to (provide) HH and CC coupling constants.
2D NMR Spectra. While the main goal of our 2D NMR development has been to produce calculated HMBC spectra, with HH coupling we can also produce COSY spectra. These (in various permutations) are the two most popular experimental 2D spectra. Previous Spartan versions have had this capability, but in the new release we will also be able to overlay the calculated spectra onto experimental spectra. Typically, the experimental data are not reported in digital form (only as PDF’s), so we are working to implement a user-friendly means of comparison. At present we have a procedure for bringing in an image of 2D spectra and fitting this range/display to calculated Spectra for comparison. Some manual manipulation is required and we are working to optimize these tools.
Energy Database. The Spartan Spectra & Properties Database (SSPD) is presently being expanded to include ωB97X-V/6-311+G(2df,2p) energies (as a property) will be available from existing ωB97X-D/6-31G* structures and NMR spectra. These energies will be accessible from the Reactions dialog.
Parallel Processing. (Parallel Suite only)
The shared memory parallelization routines which first appeared in Spartan’16 have been extended to include frequencies. Two license options will be available, an up to 16 cores (default) and a greater than 16 cores for high performance servers (or cluster nodes). Initial benchmarking done with Hartree-Fock and large basis sets reflects a factor of 40 performance increase (over single core frequencies) on a 64 core system. Additional improvements are being worked on by our partners in Q-Chem, Inc.
Each 3D structure now includes a 2D line drawing (as a property). Molecules can be constructed in 2D or 3D and modifications in either mode are maintained. A new output summary includes an exportable tabulated layout for easier data management. Graphical surfaces have been updated to include a silhouetted display style for transparent or mesh surfaces.
The standard Spartan'18 Parallel Suite license will take advantage of up to 16 cores for parallel tasks. For HPC systems, a >16 core option may also be licensed. The latest Q-Chem version will be bundled with the '18 release, providing several additional density functional models as well as ne effective core potential enabling optimizations for Lanthanides (properly accounting for f orbitals).