first principle calculation

"First principle calculation" is a method to calculate physical properties directly from basic physical quantities such as the mass and charge, Coulomb force of an electron, etc. based on the principle of quantum mechanics. In other words, the calculation derives physical properties directly from the basic principle without introducing adjusting parameters or modeling which are used to find agreement between theoretical calculations and experimental results. Starting from the Coulomb interaction between electrons, atomic nuclei and electron-atomic nucleus, the properties of materials (mainly electronic properties) are non-empirically calculated. Along with the great improvement of the computer performance, the calculations for systems containing many atoms have become possible with lower cost and high speed, thus the method is increasingly prevailing. The method is indispensable for predicting properties of new materials and of understanding properties of existing materials. In the TEM field, the method is used for the study of fine structures of EELS spectra that reflect the density of states of materials.

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