- Olah GA, Liang G (1975) J Am Chem Soc 97:6803, and references therein
- Hehre WJ, Shusterman AJ, Nelson JE (1998) The molecular modelling workbook of organic
chemistry. Wavefunction Inc., Irvine, CA - (a) Coulson’s remarks: Bolcer JD, Hermann RB (1996) In: Lipkowitz KB, Boyd DB (eds)
Reviews in computational chemistry, vol 5. VCH, New York, chapter 1, p 12. (b) The in-
crease in computer speed is also dramatically shown in data provided inGaussian
News, 1993, 4 , 1. The approximate times for a single-point HF/6–31G calculation on
1,3,5-triamino-2,4,6-trinitrobenzene (300 basis functions) are reported as: ca. 1967, on a
CDC 1604, 200 years (estimated); ca. 1992, on a 486 DX personal computer, 20 hours. This
is a speed factor of 90,000 in 25 years. The price factor for the machines may not be as
dramatic, but suffice it to say that the CDC 1604 was not considered a personal computer. In
mid-2009, on a well-endowed personal computer (ca. $4000) these results were obtained for
single-point HF/6#31G calculations on 1,3,5-triamino-2,4,6-trinitrobenzene: starting
from a C3 geometry, 23 s; starting from a C1 geometry, 42 s. The increase in speed
represented by 42 s in 2009 is, cf. 200 years in 1967, a factor of about 10^8 in 42 years; cf.
20 h in 1992, a factor of about 1,700 in 17 years
Added in press:
- Milani A, Castiglioni C (2010) Atomic charges from IR C-H stretching intensities. J Phys
Chem A 114:624 - Strain: (a) Fishtik I (2010) Challenge to a concept (protobranching) which leads to a
substantially lower strain energy for cyclopropane than the generally accepted value.
J Phys Chem A 114:3731. (b) A rebuttal to (a) Schleyer PvR, McKee WC (2010) J Phys
Chem A 114:3737 - Aihara J-I, Ishida T (2010) Aromaticity, benzene, and the role of sigma and pi bonds;
alternating-bond benzene is still aromatic. J Phys Chem A 114:1093 - Stanger A (2010) NICS: The use of plots of NICS values versus distance above the ring.
J Org Chem 75:2281 - Jablonski M, Palusiak M (2010) Atoms-in-molecules: Dependence of results on basis set was
not strong in a study of weakly H-bonded systems. J Phys Chem A 114:2240
Easier Questions.............................................................
- In the termHartree–Fock, what, essentially, were the contributions of each of
these two people? - What is a spin orbital? A spatial orbital?
- At which step in the derivation of the Hartree–Fock energy does the assumption
that each electron sees an “average electron cloud” appear? - For a closed-shell molecule the number of occupied molecular orbitals is half
the number of electrons, but there is no limit to the number of virtual orbitals.
Explain. - In the simple H€uckel method,csidenotes the basis function coefficient for the
contribution of atom numbers(in whatever numbering scheme we choose) to
MO numberi. In the ab initio method,csistill refers to MO numberi, but the
sdoes not necessarily denote atom numbers. Explain. - The derivation of the Roothaan–Hall equations involves some key concepts:
Slater determinant, Schr€odinger equation, explicit Hamiltonian operator,
388 5 Ab initio Calculations