Hartree-Fock SCF calculations

Summary of the steps in a single-point Hartree-Fock (SCF) calculation using the Roothaan-Hall LCAO expansion of the MO s... 

Hartree-Fock SCF calculation using a gaussian basis set (HF/3-21G) of the potential energy curve associated with the internal rotation of dimethylethylamine. 

For HeC ", Hartree-Fock SCF calculations were reported for the X I" ground state by Harrison et al. [91] and by Cooper and Wilson [83] who also calculated HeN and HeO ", The potential energy curves of the low-lying electronic states of HeC [8] and NeC [9] were calculated by Koch et al. using a complete active space SCF (CASSCF) approach. From these calculations it is predicted that the (X X ) ground state of HeC is thermodynamically stable with D = 16.6 kcal/mol [8] while NeC " (X X ) has a barrier for the exothermic dissociation into Ne ( P)- -C ( P) of 37.3 kcal/mol. 

Matcha and coworkers [105] also reported theoretical results based on Hartree-Fock SCF calculations for the mixed triatomic cation HeNeH". They... 

A Hartree-Fock SCF calculation with K basis functions provides K molecular orbitals, but many of these will not be occupied by any electrons they are the virtual spin orbitals. If we were to add an electron to one of these virtual orbitals then this should provide a means of calculating the electron affinity of the system. Electron affinities predicted by Koopman s theorem are always positive when Hartree-Fock calculations are used, because the virtual orbitals always have a positive energy. However, it is observed experimentally that many neutral molecules will accept an electron to form a stable anion and so have negative electron affinities. This can be understood if one realises that electron correlation would be expected to add to the error due to the frozen orbital approximation, rather than to counteract it as for ionisation potentials. 

A great deal of computation is required to perform a Hartree-Fock SCF calculation for a many-electron atom. Hartree did several SCF calculations in the 1930s, when... 

Semiempirical molecular quantum-mechanical methods use a simpler Hamiltonian than the correct molecular Hamiltonian and use parameters whose values are adjusted to fit experimental data or the results of ab initio calculations an example is the Hiickel MO treatment of conjugated hydrocarbons (Section 16.3), which uses a one-electron Hamiltonian and takes the bond integrals as adjustable parameters rather than quantities to be calculated theoretically. In contrast, an ab initio (or first principles) calculation uses the correct Hamiltonian and does not use experimental data other than the values of the fundamental physical constants. A Hartree-Fock SCF calculation seeks the antisymmetrized product d> of one-electron functions that minimizes / dr, where H is the true Hamiltonian, and is thus an ab initio calcula-... 

A restricted Hartree-Fock SCF calculation will be performed using Pulay DIPS + Geometric Direct Minimization Optimization ... 

A lot of computation is required to perform a Hartree-Fock SCF calculation for a many-electron atom. Hartree did several SCF calculations in the 1930s, when electronic computers were not in existence. Fortunately, Hartree s father, a retired engineer, enjoyed numerical computation as a hobby and helped his son. Nowadays compnters have replaced Hartree s father. 

Ho and Melius have employed Hartree-Fock SCF calculations with modest basis sets (6-31G ) with MP4(SDTQ)/6-31G perturbation theory correlation corrections at the HF/6-31G geometries and bond additivity corrections to predict revised A7/f(298 K) values (kcalmoU ) for SiF2 (—149.86 4.00) and SiHF (—35.70 2.85). Dissociation enthalpies for the formation of silylenes from S1F4, SiFs, SiHFs, S1H2F2, SiHsF, SiHF2, SiH2F and Si2Fe were also predicted. ... 

The first step in the parameterization requires performing valence ab initio Hartree-Fock SCF calculations on the model molecules by a theoretical pseudopotential method [64] with first an STO-3G minimal basis set and then a double-zeta basis set. For botli model molecules we take the Fock operator to be... 

There are no specific dieoretical reasons to expect that polarizability derivatives would be less sensitive to correlation effects. Nevertheless, die data of Amos for H2O and CH4 and to lesser extent for C2H2 [175,189] show diat near Hartree-Fock SCF calculations may provide quite acceptable values for the intensities in Raman spectra. 

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