{"id":40,"date":"2022-12-08T14:03:29","date_gmt":"2022-12-08T14:03:29","guid":{"rendered":"https:\/\/comp-chem-lab.de\/?page_id=40"},"modified":"2025-03-12T13:47:04","modified_gmt":"2025-03-12T13:47:04","slug":"faq","status":"publish","type":"page","link":"https:\/\/comp-chem-lab.de\/en\/faq\/","title":{"rendered":"background"},"content":{"rendered":"
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Theoretical Background<\/h1>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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\n\t\t\t\t\t\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/i><\/span>\n\t\t\t\t\t\t\t\t<\/i><\/span>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>\n\t\t\t\t\t\t\t\t\t\t\t\tWhat are quantum chemical experiments?<\/a>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t

Erwin Schr\u00f6dinger postulated a very important tool to calculate energies of all kinds of chemical compounds in 1926 - the so called Schr\u00f6dinger equation.<\/p>\n

\u0124 \u03a8 = E \u03a8<\/em><\/p>\n

mit E<\/em>: energy; \u03a8<\/em>: wave function, \u0124<\/em>: Hamilton operator (combination of calculations on potential and kinetic energy of a particle)<\/p>\n

Nevertheless, scientists had to determine the energy of chemical compounds and reactions by conducting effortful experiments. Why? You can only get an exact solution of the Schr\u00f6dinger equation when it is applied to the hydrogen atom. For any larger systems, numerical (approximating) methods are needed, which is extremely cumbersome. Therefore, computer with high computing capacities had to be invented. Today, it is even possible to predict the structures of complex proteins and the products of chemical reactions based on quantum chemical calculations. Experiments can not only be conducted in the laboratory but also by using computers. Since computer chips mainly consist of silicon, experiments that are conducted with computers are called in silico<\/i> experiments.<\/p>\n

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Erwin Schr\u00f6dinger<\/em><\/p><\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t\t\t

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\n\t\t\t\t\t\t\t\t\t\t\t\t\t\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/i><\/span>\n\t\t\t\t\t\t\t\t<\/i><\/span>\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/span>\n\t\t\t\t\t\t\t\t\t\t\t\tI want to know more: How do I calculate the energy of different structures?<\/a>\n\t\t\t\t\t<\/div>\n\t\t\t\t\t

To get a first idea of the way computer chemical methods work, we need to take a closer look at the Schr\u00f6dinger equation:<\/p>

\u0124 \u03a8 = E \u03a8<\/em><\/p>

E stands for the energy which is to be calculated and\u00a0 \u03a8 <\/em>represents the so called wave function. The Hamilton operator corresponds to the energy of the whole system. To simplify the equation, one assumes that the nuclei of the atoms are more or less immobile (Born-Oppenheimer approximation). The Hamilton operator then includes the following parameters:<\/p>