By 1971, when a bibliography of ab initio calculations was published, the largest molecules included were naphthalene and azulene. The first configuration interaction calculations were carried out in Cambridge on the EDSAC computer in the 1950s using Gaussian orbitals by Boys and coworkers. The first polyatomic calculations using Gaussian orbitals were carried out in the late 1950s. For diatomic molecules a systematic study using a minimum basis set and the first calculation with a larger basis set were published by Ransil and Nesbet respectively in 1960.
The first ab initio Hartree-Fock calculations on diatomic molecules were carried out in 1956 at MIT using a basis set of Slater orbitals. A very detailed account of such use in the United Kingdom is given by Smith and Sutcliffe. Theoretical chemists became extensive users of the early digital computers.
In the early 1950s, the first semi-empirical atomic orbital calculations were carried out.
With the development of efficient computer technology in the 1940s the solutions of elaborate wave equations for complex atomic systems began to be a realizable objective. Bright Wilson’s 1935 Introduction to Quantum Mechanics – with Applications to Chemistry, Eyring, Walter and Kimball's 1944 Quantum Chemistry, Heitler’s 1945 Elementary Wave Mechanics – with Applications to Quantum Chemistry, and later Coulson's 1952 textbook Valence, each of which served as primary references for chemists in the decades to follow. The books that were influential in the early development of computational quantum chemistry include: Linus Pauling and E. 4 Interpreting molecular wave functionsīuilding on the founding discoveries and theories in the history of quantum mechanics, the first theoretical calculations in chemistry were those of Walter Heitler and Fritz London in 1927.3.3 Semi-empirical and empirical methods.The less accurate methods are called empirical or semi-empirical because some experimental results, often from atoms or related molecules, are used along with the theory. The accurate methods used are called ab initio methods, as they are based entirely on theory from first principles. The methods are thus based on theories which range from highly accurate, but are suitable only for small systems, to very approximate, but suitable for very large systems. That system can be a single molecule, a group of molecules or a solid. In all cases the computer time increases rapidly with the size of the system being studied. The methods employed cover both static and dynamic situations. the expected positions of the constituent atoms), absolute and relative (interaction) energies, electronic charge distributions, dipoles and higher multipole moments, vibrational frequencies, reactivity or other spectroscopic quantities, and cross sections for collision with other particles. It is widely used in the design of new drugs and materials.Įxamples of such properties are structure (i.e. While its results normally complement the information obtained by chemical experiments, it can in some cases predict hitherto unobserved chemical phenomena. It uses the results of theoretical chemistry, incorporated into efficient computer programs, to calculate the structures and properties of molecules and solids. Computational chemistry is a branch of chemistry that uses computers to assist in solving chemical problems.
0 kommentar(er)
