Torsion force constants

Th c values of V I, V2, and V3, in keal/tnol, are listed in mmp-tor.txtfdbf). fhc MM+ force field uses special values for the torsional force constants when the atoms are in a four-member ring. 

The 3-atom and 4-atom restraints behave just like those for two atoms, except that the dialog box requests an angle rather than a distance and the accompanying request for a force constant requires either a bending force constant (3-atom case) or a torsional force constant (4-atom case). 

Propene and cis-butene-2 possess the molecular symmetries C2 and C2 v (28, 29), respectively. (Fig. 4 the geometry parameters given are derived from force field calculations (19, 30) and agree well with experiment.) The barriers // observed for the rotation of the methyl groups amount to 1.98 kcal mole-1 for propene (28), and 0.75 kcal mole-1 for cis-butene-2 (29). The torsional force constants K for the methyl groups... 

The value of the velocity for g = 0 is very small. This calculation at g = 0 did include reasonable values for torsion force constants. The nonbonded interactions are essential to fit observed velocities. 

Calculation of the critical lateral force is more complicated because traditional LFM does not provide us with easy method to translate current units into force ones. There is no way to define the factor of proportionality until calibration algorithm was developed recently by ourselves [8], The required coefficient depends on design of a microscope, adjustment of the optical system, torsion force constant kL of cantilever and tip height lnp. 

To determine torsion force constant and height of tip we didn t refer to cantilever passport parameters that can be significant varied. The value of kL we found used new the most precise method based on analyzing of amplitude-phase characteristic [to be published] but tip height was determined with the help of optical microscope. We got kL = 77.1 N/m ltip = 10 pm. 

The INS spectra of a series of ethene complexes were determined in the low frequency region (below 800 cm ) [74, 75, 76]. The interest was the torsional motions of ethene bound at a metal center. Peak positions and assignments are given in Table 7.10. The torsional force constants were calculated. 

The strategy we have taken in the determination of the stretching force constants is as follows First, we determined a complete set of force constants in the S0 state, including the stretching, in-plane bending, out-of-plane wagging, and torsional force constants of Urey-Bradley-Shimanouchi (UBS) type, and also, non-UBS cross-terms, many of which were transferred from those determined by Saito... 

Fully quantitative measurements using shear modulation have most of the challenges encountered in other SFM experiments including determination of bending, buckling and torsional force constants of the cantilever, the true shape of the probe tip, and creep and hysteresis in piezoelectric response. Here we emphasize three essential considerations that should be made in designing shear modulation experiments for SFM. 

Generally, only a small number of scaling constants are needed. For example, ten scaling constants and reference values were derived for hydrocarbons from comparisons of gas phase structures, conformational energies, rotational barriers, and vibrational frequencies measured by experiment and calculated by the QMFF. For the bond and bond angle energy functions in equation (1) the same scale factor is multiplied by the QMFF quadratic, cubic, and quartic force constants. Similarly, the same scale factor is used for the one-, two-, and threefold torsion force constants, and a single scale factor is used for all cross terms. 

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