Single point energy calculation

Within some programs, the ROMPn methods do not support analytic gradients. Thus, the fastest way to run the calculation is as a single point energy calculation with a geometry from another method. If a geometry optimization must be done at this level of theory, a non-gradient-based method such as the Fletcher-Powell optimization should be used. 

Single point energy calculations are performed for many purposes, including the following ... 

Single point energy calculations can be performed at any level of theory and with small or large basis sets. The ones we ll do in this chapter will be at the Hartree-Fock level with medium-sized basis sets, but keep in mind that high accuracy energy computations are set up and interpreted in very much the same way. 

Setting up an input file for a Gaussian single point energy calculation follows the steps we used in the Quick Start. To request this type of calculation, you must supply the following information ... 

Here are some other useful keywords for single point energy calculations (and other types of jobs as well) ... 

Here we give the molecule specification in Cartesian coordinates. The route section specifies a single point energy calculation at the Hartree-Fock level, using the 6-31G(d) basis set. We ve specified a restricted Hartree-Fock calculation (via the R prepended to the HF procedure keyword) because this is a closed shell system. We ve also requested that information about the molecular orbitals be included in the output with Pop=Reg. 

Run a single point energy calculation on propene and determine the following information from the output ... 

Make a table of the energies and dipole moments for the three stereoisomers of l,2-dichloro-l,2-difluoroethane (stoichiometry CHFCl-CHFCl). You ll need to set up and run a HF/6-31G(d) single point energy calculation for each form. 

Here are the results we obtained by running these hydrocarbon single point energy calculations on a DEC AlphaStation 600 computer (in CPU seconds). In the table, N is the number of carbons in the system ... 

Run a single-point energy calculation on methanol using the HF/6-31++G(d,p) model chemistry, including the GFPrint and GFinput keywords in the route section which request that the basis set information be included in the output file (in tabular and input format, respectively). Examine the basis set output and identify its main components. 

By convention, n must be greater than nn for a system with an od number of electrons. Also, this counting should ignore the core electrons i the molecule (these are treated in step 6). Gaussian will indicate the numbt of electrons of each type. Look for the line containing NOB in the outpt from the single point energy calculation in step 3 ... 

We ran an SCRF single point energy calculation for gauche dichloroethane conformers in cyclohexane (e=2.0), using the Onsager model at the Hartree-Fock and MP2 levels of theory (flfl=3.65) and using the IPCM model at the B3LYP level. The 6-31+G(d) basis set was used for all jobs. We also ran gas phase calculations for both conformations at the same model chemistries, and an IPCM calculation for the trans conformation (SCRF=Dipole calculations are not necessary for the trans conformation since it has no dipole moment). 

For a given set of nuclear coordinates, this corresponds to the total energy predicted hy a single point energy calculation, although such calculations, of course, do not solve this equation exactly. The approximation methods used to solve it will be discussed in subsequent sections of this appendix. 

Chapter 2, Single Point Energy Calculations, discusses computing energies at specific molecular structures, as well as the related molecular properties that may be predicted at the same time. 

Molecular geometries, which were not reported in this study, have been obtained using the 6-31 G(d,p) and cc-pVDZ basis sets. Thus, the 6-31 lG(d,p) and cc-pVTZ results refer to single point energy calculations only. 

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