Brief History of Computational Chemistry

www.gsjpublications.com Global Scientific Global Scientific Journal of Chemistry Journal of 3 (1) 2020/ 18-22 Chemistry www.gsjpublications.com/gsjc Brief History of Computational Chemistry Nidaa A. Jasim Physical Chemistry, Directorate of Education, Karbala, Iraq. Email Address: [email protected] Received: 2 Oct 2020, Revised: 7 Oct 2020, Accepted: 16 Oct 2020, Online: 13 Nov 2020 Abstract Computational Chemistry is a broad and multifaceted branch of chemistry. It can generally be distinguished by using physics, mathematics, and computers to understand all aspects of chemistry: such as properties of substances and the properties of elements and molecules and their interactions, or to simulate molecular phenomena, or to predict properties of new molecules or phases of matter, Computational chemistry relies on creating an effective mathematical approximation to solve experimental chemistry problems for complex compounds through the use of advanced computer programs at lower cost and faster speed, developing algorithms and making approximations and neglecting integrals in order to arrive at the properties of molecules and in an approximate manner such as total energy, dipole moment, vibrational and reactive frequencies and other spectral properties, and arrive at various minute atomic and subatomic details. Computational chemistry is considered an overlap between computer science and chemistry in order to provide quick and urgent solutions to some complex problems facing chemists and physicists to help them solve laboratory problems.This article deals with a scientific review of the development of computational chemistry, starting with Schrödinger’s equations and the accompanying development of computers and their use by chemists and physicists and the impact of chemistry science with the advancement of computer software and the explosion of knowledge in information technology. The article dealt with the most important software packages used in computational chemistry, the stages of updating them, the difficulties faced by chemists and their attempts to solve complex Schrödinger equations and provide theoretical treatments based on the use of approximations and neglect of some integrals and the types of methods used in quantum chemistry, including AB Initio, which provides us with accurate information about some interactions Chemical that was difficult to follow in the laboratory And methods Semi- empirical that give us less accurate information. Keywords: Brief History, Computational Chemistry, Chemistry 1. Introduction History of Computational Chemistry Bohr's atomic theory. Schrödinger benefited from his experience in In late 1925 Schrödinger developed a mathematics and from De Brogleie's differential equation describing the change suggestions and was able to write his of a physical state with time in order to famous wave equation and his study that overcome the difficulties that appear in Jasim, N. A. Global Scientific Journal of Chemistry 2020/ 3 (1) 19 depends on the wave is called quantum term molecular orbital was introduced by mechanics [1], [2] . Robert Mulliken and the molecular orbital theory became accepted in 1933 as a valid In 1926 And soon after quantum chemistry and useful theory. Hückel was able to use appeared, Paul Dirac explained that the the orbital theory in terms of Quantitative, Schrödinger equation and the laws of based on Lennard Jones' paper [8]. physics can only be applied to simple atoms and molecules such as H, He, H2 During the thirties of the last century and H2+ and The mathematical solution to (1936-1938) the first electromechanical the Schrödinger equation is impossible due computer was invented, and then in 1942 to the difficulty of it. Therefore, theorists an electric computer was invented, so have tried for decades to propose chemists were able to develop a number of mathematical models to calculate the wave computational models to compute a wave function of material by approximate function of modulation in approximate methods. Where Dirac presented the ways [9]. These methods can be arranged number of wave functions for four hierarchically from Hartree- Fok At the complex numbers, in contrast to the bottom of the hierarchy, the less subtle to Schrödinger equation, which describes the the more accurate methods, this success wave function of a single compound has led to the modeling of electronic [3],[4]. behavior in multi-electron molecules .From (1940-1950), electronic computers In the late twenties and early thirties, the were developed by some chemicals British Hartree and the Russian Fock developed an effective method for solving While computer became available for multiple electron problems and called it general use by chemists and physicists of the Hartree- Fock method. It is an iterative the twentieth century (4). In 1955 the HF method and during repetition the average and LCAO chains were linked - MO by electron interaction is calculated. This Clemens CJ Roothaan who was able to method uses the approximate wave write HF equations based on small orbitals function and energy levels in the multi- [10]. electron atoms [5]. (By observing Pauli's exclusion principle). According to this In 1964 Hückel was able to determine the method, the functions of the elementary electron orbital energy in complex wave can be considered as hydrogen hydrocarbon compounds such as butadiene atomic orbitals, and the resulting equations and benzene using a simple linear can be solved numerically using a combination of the atomic orbitals method computer [6]. Sir John Edward and (LCAO) and computers, and the Lennard Jones( 1929 )linear combination experimental methods were replaced by of atomic orbital , or LCAO-MO, were quasi-experimental methods such as developed, a quantum superposition of CNDO [11]. After advances in computer orbitals and a technique for computing technology in the mid-1960s, Robert molecular orbitals in quantum chemistry, Mulliken was able to receive the Nobel and these wave functions are the basic Prize in 1966 for his development of the functions, which describe electrons[7]. theory of molecular orbit. Robert Mulliken was able to use computers in calculations Friedrich Hund, Robert Mulliken, John of the electronic structure of molecules. Slater, and Lenard attempted were Robert Mulliken while receiving the Nobel developed the molecular orbital theory in Prize, announced the major in the years following the establishment of computational chemistry as a recognized the valence bond theory and mainly the specialty. From that time on, theoretical Jasim, N. A. Global Scientific Journal of Chemistry 2020/ 3 (1) 20 computational chemistry began to be used community, and developed another to study complex chemical problems that program Q-Chem, for which he described were difficult to study in chemistry the Gaussian molecular orbital method in laboratories [12] the 1986 book Ab Intio by Leo Radom and Warren Hehre, Paul Schleier and Bebel. The structures of molecules and the way Then, despite the controversy, Popple they interact with each other depend on the returned to update the Gaussian70 program calculations of quantum chemistry. to Gaussian09 and Gaussian09W, and this However, the calculations of quantum program has been used in chemical chemistry are very complex, especially for laboratories by chemists, physicists and multi-electron particles so in the 1960s, engineers to solve many complex Pople and his research group (1960s) equations. This program uses quantum attempted to develop a number of chemistry calculations to provide algorithms that provided vital inputs to the predictions of the properties of molecules computations, including a Gaussian and their behavior in chemical reactions as computer program that provides well as spectroscopic data (NMR, IR, UV, experimental data (rule groups 3IG-6, 6- et (. The Gaussian program continued to be 31G.) This program can provide a updated for 40 years, leading to Gaussian description of the properties of the 16, which is the latest in a series of molecules and the chemical pathway [13], Gaussian programs [16]. This advanced John also worked with his research group program can study all large-sized and during the 1970s on the 3IG-6, 6-31G base multi-electron molecular systems and groups. Pople (1979) was a pioneer in provides accurate information about computational chemistry programs, and his electronic systems. It has been licensed most notable achievement was paper with from different computers and does not Gavachari and Pinkley in which they impose any restrictions on the operations presented a practical algorithm. of the Gaussian 16 In addition, The Gaussian view 6 program has been added Pople was a leader in developing to provide support for all the features of computational methods for solving Gaussian 16 and to increase its vital complex multi-electron systems called capabilities [17]. quantum chemistry methods Ab initio and using basic sets of orbits of the Slater orbit In the 1990s and specifically, 1993: More type or Gaussian orbitals to model the modern functions are added(GGA's and wave function. These calculations were hybrids) to thermochemistry. In 1995: very expensive in the early period of their TDDFT and hybrid DFT methods were use. However, continuous processors made added, and in 1998 the Pople and Walter them very accurate and fast, and today Kuhn won the Nobel Prize. they are very useful in developing most computer chemistry software packages. In Pebel for development of computational 1970, for the first

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