Contemporary computers, power

The various basis sets used in a calculation of the H and S integrals for a system are attempts to obtain a basis set that is as close as possible to a complete set but to stay within practical limits set by the speed and memory of contemporary computers. One immediately notices that the enterprise is directly dependent on the capabilities of available computers, which have become more powerful over the past several decades. The size and complexity of basis sets in common use have increased accordingly. Whatever basis set we choose, however, we are attempting to strike a balance. If the basis set is too small, it is inaeeurate if it is too large, it exceeds the capabilities of our computer. Whether our basis set is large or small, if we attempt to calculate all the H and S integrals in the secular matrix without any infusion of empirical information, the procedure is described as ab initio. 

Calculations based on ab initio methods of molecular electronic structure theory are very demanding computationally and any review of progress over the past two decades must be made against the background of the continually increasing power of contemporary computers. The past 20 years have witnessed a relentless increase in the power of computing machines. It has been observed that the processing power of computers seems to double every 18 months. As the historian Roberts [100] points out in his book Twentieth Century... 

The solution of detailed n-fluid model for complex geometry and physics is challenging even with contemporary high-power computing machines. Further, presence of a large number of constitutive relations makes this model dependent on the accuracy of these relations. Therefore, a number of assumptions must be made to simplify the n-fluid model depending on the complexity of the physical picture adopted. 

The operator skill required to perform reliable measurements using bridge circuits and the 2-meter was appreciable and the contemporary desire for digital display, the availability of cheap computing power, and improvements in electronic circuit reliabihty have led to the replacement of these instruments by impedance or LCR meters. In operation, either an Ohm s law or a ratio process is used, the latter being an inherently more precise technique, but requiring a more sophisticated switching process. 

Electrical and electronic devices and machines have become an integral part of contemporary life, ranging from household appliances and computers to huge industrial machines. Wlien home and business owners pay the monthly bill from the electrical power company for the use of all of these items, they arc paying for energy very conveniently delivered over electrical wires from the power company. 

Aromaticity has generally been recognized from an examination of experimental facts, as was shown previously. Many criteria for aromaticity have been proposed over the years prominent in contemporary studies are criteria based on magnetic properties. The inquiry is also currently moving from experimental methods to those that employ the power of modern computational methods, especially as applied to magnetic phenomena. Prominent and widely accepted among computational methods is that introduced by Schleyer et al. in 1996. This method is based on magnetic properties associated with cyclic electron... 

A fiindamaital goal of Materials Sdence and Tedinology is to relate the mio oscoi (molecular) structure of a material to its macroscopic (structural, imchanical, dynamic, thermodynamic) properties, and to be able to predict the diange of these macroscopic properties upon the introduction of chemical mc ific tions at the microscopic level. This is one of the key-problems of contemporary Materials Science and in its solution computer simulation has been estaUished as a powerful tool [1-4]. 

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