Jaguar is an ab initio quantum chemical program that specializes in fast electronic structure predictions for molecular systems of medium and large size. Jaguar focuses on computational methods with reasonable computational scaling with the size of the system, such as density functional theory (DFT) and local secondorder Mïller-Plesset perturbation theory. The favorable scaling of the methods and the high efficiency of the program make it possible to conduct routine computations involving several thousand molecular orbitals. This performance is achieved through a utilization of the pseudospectral approximation and several levels of parallelization. The speed advantages are beneficial for applying Jaguar in biomolecular computational modeling. Additionally, owing to its superior wave function guess for transition-metalcontaining systems, Jaguar finds applications in inorganic and bioinorganic chemistry. The emphasis on larger systems and transition metal elements paves the way toward developing Jaguar for its use in materials science modeling. The article describes the historical and new features of Jaguar, such as improved parallelization of many modules, innovations in ab initio pKa prediction, and new semiempirical corrections for nondynamic correlation errors in DFT. Jaguar applications in drug discovery, materials science, force field parameterization, and other areas of computational research are reviewed. Timing benchmarks and other results obtained from the most recent Jaguar code are provided. The article concludes with a discussion of challenges and directions for future development of the program.

The inelastic neutron scattering spectra of the polycrystalline n-alkanes, 5<n<25, have been obtained at ∼25 K. At this temperature the n-alkane molecules are extended in their all-trans configuration. The spectral region from 200 to 600 cm−1 is reported with emphasis on the higher frequency longitudinal acoustic modes (LAM). These modes are identified by their nominal translational symmetry eigenvector, κ. A complete assignment of experimental frequencies out to κ≈0.7 is presented for the first time. This assignment is consistent with the known optical data and ab initio Hartree–Fock and DFT calculations. On the basis of these theoretical results, the lower frequency, higher κ LAM modes are also assigned. The LAM sequences exhibit bandhead behavior, i.e., a maximum frequency value, vmax, at some value of κ. The maximum frequency is consistently found at κmax=0.36±0.01 [cf. polyethylene (PE), κmax=0.34] for all chain lengths but the value of the maximum frequency, vmax, increases roughly linearly with n for n>7. At about n=21 it reaches the value found for PE, 525 cm−1. This variation in frequency with chain length for the same nominal value of κ and also the full set of calculated DFT LAM results is compared with the expectations of a simple zig–zag bead bending model.

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Time-dependent density functional theory (TDDFT) is implemented within the Tamm-Dancoff approximation (TDA) using a pseudospectral approach to evaluate two-electron repulsion integrals. The pseudospectral approximation uses a split representation with both spectral basis functions and a physical space grid to achieve a reduction in the scaling behavior of electronic structure methods. We demonstrate here that exceptionally sparse grids may be used in the excitation energy calculation, following earlier work employing the pseudospectral approximation for determining correlation energies in wavefunction-based methods with similar conclusions. The pseudospectral TDA-TDDFT method is shown to be up to ten times faster than a conventional algorithm for hybrid functionals without sacrificing chemical accuracy.

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We have developed an algorithm based upon pseudospectral (PS) ab initio electronic structure methods for evaluating nuclear magnetic shielding constants using gauge-including atomic orbitals (GIAOs) in the spin-restricted and spin-unrestricted formalisms of Hartree-Fock (HF) theory and density-functional theory (DFT). The nuclear magnetic shielding constants for both 1H and 13C calculated using PS methodology for 21 small molecules have absolute mean errors of less than 0.3 ppm in comparison with analytic integral results. CPU timing comparisons between PS methods and conventional methods carried out for seven large molecules ranging from 510 to 1285 basis functions demonstrate that the PS methods are an order of magnitude more efficient than the conventional methods. PS-HF was between 9 and 26 times faster than conventional integral technology, and PS-DFT (Becke three-parameter Lee-Yang-Parr) was between 6 and 21 times faster.

The dynamics and bonding of the hydrido complex Ba[ReH9], containing the D3h face-capped trigonal prismatic [ReH9]2- ion, have been investigated by vibrational spectroscopy and density functional theory (DFT). The combination of infrared, Raman, and inelastic neutron-scattering (INS) spectroscopies has enabled observation of all the modes of the [ReH9]2- ion for the first time. We demonstrate that calculations of the isolated [ReH9]2- ion are unable to reproduce the INS spectrum and that the complete unit cell must be considered with periodic DFT to have reliable results. This is shown to be a consequence of the long-range Coulomb potential present. Analysis of the electronic structure shows that the bonding between the rhenium and the hydrogen is largely covalent. There is a small degree of covalency between the prism hydrides and the barium. The counterion is crucial to the stability of the materials; hence, variation of it potentially offers a method to fine-tune the properties of the material.

We present a methodology for computing the binding energy of molecular dimers based on extrapolation of pseudospectral local second-order Moller-Plesset (MP2), or PS-LMP2, energies to the basis set limit. The extrapolation protocol is based on carrying out PS-LMP2 calculations with the Dunning cc-pVTZ (-f) and cc-pVQZ (-g) basis sets and then using a simple two-parameter function to compute the final basis set limit results. The function is parametrized to ultralarge basis set MP2 calculations for 5 molecular pairs taken from the literature and then tested by calculating results for a set of formamide dimers for which such calculations have also been carried out. The results agree to within ca. 0.2 kcal/mol with the conventional MP2 large basis set calculations. A specialized, but relatively simple, protocol is described for eliminating noise due to overcompleteness of the basis set. Timing results are presented for the LMP2 calculations, and comparisons are made with the LMP2 methodology of the QChem program. CPU time required by each of the methods scales as N(3), where N is the number of the basis functions, with the PS-LMP2 approach displaying a 2- to 3-fold advantage in the prefactor. We also discuss one set of test cases for which the PS-LMP2 results disagree with those obtained from an alternative type of MP2 calculation, N-methyl acetamide (NMA) dimers, and show that the results for liquid-state simulations using polarizable parameters derived by fitting to the PS-LMP2 binding energies appear to produce better results when compared with experimental data. The convergence issues associated with the alternative MP2 formulation remain to be investigated.