Henry F. Schaefer

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This does not exclude the possibility, that larger structural fragments (such as tetra-mers and pentamers) can also contribute to the low-frequency vibrational spectrum around the boson peak. On the basis of these results, the following model of the glass transition of glycerol can be proposed. At temperatures far above Tg (186 K), the lifetime of the MRO(More)
Advances in theory and algorithms for electronic structure calculations must be incorporated into program packages to enable them to become routinely used by the broader chemical community. This work reviews advances made over the past five years or so that constitute the major improvements contained in a new release of the Q-Chem quantum chemistry package,(More)
A hybrid quantum mechanical/molecular mechanical (QM/MM) potential energy function with Hartree-Fock, density functional theory (DFT), and post-HF (RIMP2, MP2, CCSD) capability has been implemented in the CHARMM and Q-Chem software packages. In addition, we have modified CHARMM and Q-Chem to take advantage of the newly introduced replica path and the nudged(More)
The complete quartic force field of BH(3) has been converged to the ab initio limit by extrapolation of core-valence correlation-consistent basis set series (cc-pCVXZ, X = T, Q, 5) of all-electron CCSD(T) (coupled-cluster singles and doubles with perturbative triples) energy points. Additional computations including full coupled-cluster treatments through(More)
Several modifications to the Davidson algorithm are systematically explored to establish their performance for an assortment of configuration interaction (CI) computations. The combination of a generalized Davidson method, a periodic two-vector subspace collapse, and a blocked Davidson approach for multiple roots is determined to retain the convergence(More)
Ahatraet-A program of research designed to test the suitability of minicomputers for large scale scientific computations is described. The scientific problems to be attacked are those traditionally reserved for the largest and fastest commerciallv available electronic commuters: the calculation of potential energy surfaces and subsequent evaluation of the(More)
B3LYP/6-311+G** (and MP2/6-311+G**) computations, performed for a series of Diels-Alder (DA) reactions, confirm that the endo transition states (TS) and the related Cope-TSs are favored energetically over the respective exo-TSs. Likewise, the computed magnetic properties (nucleus-independent chemical shifts and magnetic susceptibililties) of the endo- (as(More)
The 2'-deoxyguanosine-3',5'-diphosphate, 2'-deoxyadenosine-3',5'-diphosphate, 2'-deoxycytidine-3',5'-diphosphate and 2'-deoxythymidine-3',5'-diphosphate systems are the smallest units of a DNA single strand. Exploring these comprehensive subunits with reliable density functional methods enables one to approach reasonable predictions of the properties of DNA(More)
Dative, or nonoxidative, ligand coordination is common in transition metal complexes; however, this bonding motif is rare in compounds of main group elements in the formal oxidation state of zero. Here, we report that the potassium graphite reduction of the neutral hypervalent silicon-carbene complex L:SiCl4 {where L: is:C[N(2,6-Pri2-C6H3)CH]2 and Pri is(More)