Force saving

One side effect of changing the interval is that you must SYS 739 repeatedly to do a forced SAVE. For example, if you change the counter value to 2, you must SYS 739 twice to do a forced SAVE, and three times if the counter is set to 3. To avoid this problem, here s a simpler way to force a SAVE when the counter is set to 2 or higher ... 

SymApps converts 2D structures From the ChemWindow drawing program into 3D representations with the help of a modified MM2 force field (see Section 7.2). Besides basic visualization tools such as display styles, perspective views, and light source adjustments, the module additionally provides calculations of bond lengths, angles, etc, Moreover, point groups and character tables can be determined. Animations of spinning movements and symmetry operations can also he created and saved as movie files (. avi). 

To redefine an atom type associated with a force field, adpist the rules in th e ch cm, ru 1 file to represent the new ehernical environment for a particular type and then compile the new types. It is always desirable to save the origin a I eh cm. nil un dcr an oth cr n am c prior to modifying chem.rul. Having modified chem. nil, you can... 

Using PCMODEL, draw H2O. Minimize using the MM3 force field. Save to the filename water.inp (or some such) in the GAMESS format. Copy to your GAMESS directory. Copy to filename INPUT and be sure that PUNCH has been renamed to PUNCH.OLD or has been erased entirely. Run using GAMESS.EXE > FILENAME.OUT. The INPUT file... 

Force field calculations often truncate the non bonded potential energy of a molecular system at some finite distance. Truncation (nonbonded cutoff) saves computing resources. Also, periodic boxes and boundary conditions require it. However, this approximation is too crude for some calculations. For example, a molecular dynamic simulation with an abruptly truncated potential produces anomalous and nonphysical behavior. One symptom is that the solute (for example, a protein) cools and the solvent (water) heats rapidly. The temperatures of system components then slowly converge until the system appears to be in equilibrium, but it is not. 

State-of-the-Ahi Control. Computer control using feed-forward capabiUty can save 2—20% of a unit s utiUties by reducing the margin of safety (5). Unless the discipline of a controller forces the reduction of the safety margin, operators typically opt for increased safety. Operators are probably correct to do so when a proper set of analy2ers and controllers has not been provided and maintained. 

Perhaps, even more important, is the stagnation in our safety and environmental performance in the last five years. Until five years ago, we had seen dramatic year on year improvement in every aspect of safety and environmental performance. This has slowed down in all areas and ceased altogether in occupational safety. I expect that these changes will invigorate all our programs. Our current safety and environmental performance costs us at least 30 million each year in avoidable costs such as capital damage and clean-up costs. If we could put a dollar value on injuries to our work-force, the savings would likely be ten times this amount. 

Some force fields use the so-called united atom approach where (for example) a methyl group is treated as a single pseudo-atom. They arose historically in order to save computer resource when dealing with large systems such as amino-acid chains. 

For a given large molecule, there are very many more non-bonded interactions than bonded ones. Molecular-mechanics force fields often truncate the non-bonded interactions at some finite distance, in order to save on computer resource. A number of ingenious algorithms have been proposed in order to ensure the continuity of the potential at the cut-off point. 

Suppose now that we build a series of cells, alike in all respects save that the (very dilute and completely dissociated) solute has a different concentration in each cell. If the cells are alike in all other respects, the unitary terms must be the same in each coll the values of the e.m.f. for the various cells will differ owing to the difference in the communal terms. In very dilute solutions the contribution made to each communal term by the interionic forces will be small, and the dependence of the e.m.f. on the concentration will arise almost entirely from the cratic term which, for each solute species, may be written — kT In y or — IcT In x. Since we are considering a uni-univalent solute, the numerical values of y+ and t/ for the positive and negative ions will both be the same as the mole ratio of the solute. 

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