Chapter 75: Determine the synthesis scheme

　　 After dinner, Xu Qiu did not go to the laboratory, but returned to the bedroom early.
　　 There is no one in the dormitory, Ren Bin probably hasn't returned to school yet, Tao Yan doesn't know where he has gone.
　　 Did he go to the laboratory too? Today is Sunday.
　　 Forget it, leave him alone.
　　 Xu Qiu lay on the bed, entered the simulation laboratory, and opened the system interface.
　　Senior Sister's DFT skill proficiency is only 50% of Tier 3, and if you want to perform 100% deduction of Tier 5, you need to upgrade first.
　　 "The system deduces DFT proficiency to level five."
　　【DFT to the fifth order 0%, 50%100+1000=1050 points are required. Is it deduced? 】
　　 "Deduction."
　　【The deduction is successful. 】
　　 "The system costs 500 points, redeemable for one fifth-order 100% DFT teaching, limited polymer analysis."
　　【The exchange is successful. 】
　　 A virtual image appears.
　　 Before using the DFT simulation software, the simulation villain typed a piece of mysterious code, put the generated file in the root directory of the software, and then opened the software.
　　 A new plug-in appeared next to the software interface, and the simulation villain entered many parameters into it.
　　 Finally, he imported the molecular structure of a single structural unit of the polymer and ran the software.
　　 About twenty minutes later, the computer got the simulation result, and Xu Qiu fast-forwarded the calculation process.
　　 He found a serious problem.
　　 That is, the polymer macromolecule demonstrated by the simulated villain is quite different from the molecular structure of the conjugated copolymer used in organic photovoltaic materials.
　　 Xu Qiu is a little bit annoyed, but it is still sloppy. It should be more specific, such as limiting the analysis of conjugated copolymers.
　　 But he didn't give up, he kept watching, and when he encountered a structure that he didn't want, he would fast forward to the next one.
　　 Fortunately, it didn't take long for him to scan only a dozen fragments, and he obtained a high-level simulation calculation method for conjugated copolymers.
　　 He recorded the mysterious code and parameters into the large computer in the simulation laboratory.
　　 Although he does not fully understand the specific functions of these codes and parameters, it does not prevent him from using them directly.
　　……
　　 Xu Qiu quit the high-level teaching video and returned to the simulation laboratory, planning to try the advanced version of DFT simulation.
　　After thinking for a moment, he decided to try the water with the classic PTB7-TH molecule.
　　 He also copied his laptop into the simulation laboratory, opened the Chemdraw software, and drew the two structural units of PTB7-TH.
　　 Among them, D unit is BDT, A unit is TT.
　　 Then import the molecular structure into a large computer, set the parameters, and start the simulation.
　　 After more than twenty minutes, the calculation is complete.
　　 The speed is a bit slow, Xu Qiu wondered, maybe I can find a high-performance computer to help him do simulation calculations, the one that can get results in seconds is the best.
　　 "The system, can you help me copy Taiwan Supercomputing?"
　　 [Insufficient authority, request to be rejected, the current host can only copy items and skills within 10 meters. 】
　　 Okay, it doesn't seem to work.
　　 Moreover, he did not have the opportunity to contact the supercomputing center in the short term. As far as he knows, there are seven supercomputing centers in the country, but none of them are in the magic capital.
　　 However, he can take second place.
　　 Go to the school to do computational physics, computational chemistry or computational materials laboratory, and a server capable of high-performance computing should be enough for the time being.
　　 For example, Mr. Wei told Professor Pei Zicai in the 219 office to do "first-principles calculations for inorganic semiconductor materials and dielectric materials."
　　 Xu Qiu has taken Pei Zicai's "Computational Materials" course. This teacher is quite interesting.
　　 When he was in class, he always couldn't help but laugh. He couldn't control his facial expression very well, so his classmates called him "Peihaha" in private.
　　……
　　While waiting for the calculation results, Xu Qiu also found a lot of literature about PTB7-TH, and summarized the various properties of PTB7-TH, mainly energy level and band gap.
　　 After comparing with the literature, it is found that there is still a certain gap between the simulated data and the actual data, and the deviation value is about 0-0.4 electron volts.
　　 Compared with the original unimproved version, the gap is very small.
　　 The original DFT simulation, because the macromolecular material is calculated as a small molecule material, the error of the measured energy level is usually above 0.5 eV, and the error of the band gap even exceeds 1 eV.
　　 You need to know that for suitable photovoltaic materials, the band gap is between 1 and 2 electron volts. This error is close to 50%, and it can't even be said to be an error.
　　 This is also the reason why senpai said that this method is used less and less.
　　 Regarding the small error that still exists after the improved version, Xu Qiu also considered the possible reasons:
　　 On the one hand, a molecule like PTB7-TH, one of its structural units, TT, is not axisymmetric, so its arrangement in macromolecules is uncertain.
　　 If all the TT units are arranged in one direction, the resulting macromolecular material will have stronger crystallization performance, smaller band gap, and generally better performance.
　　 On the contrary, if it is arranged randomly, the performance of the material is poor.
　　 On the other hand, he has studied "Organic Chemistry" and knows that synthetic reactions have side reactions.
　　 Ideally, you want small molecular units to be connected hand in hand in a straight line to form a straight macromolecular chain.
　　 But the actual situation may be that some people are holding other people's feet~EbookFREE.me~Some people have their hair caught by others, and some people have broken arms and legs.
　　 Although the possibility of the above situation is very small, maybe only 1%-5%.
　　 But for tens of hundreds of such people, there will always be various accidents, resulting in the final material is not the ideal material, but there are defects.
　　 Therefore, the results obtained by theory still need to be tested by practice after all.
　　……
　　 Xu Qiu uses software to draw the molecular structure in his idea, and then performs advanced DFT simulation calculations.
　　 A unit he chose the simple structure of benzothiadiazole BT unit, D unit chose thiophene, from one thiophene to four connected thiophenes, respectively T, 2T, 3T, 4T.
　　 The simulation calculation takes one and a half hours, and he turned on the acceleration twice.
　　 During this time, because he couldn't leave the simulation laboratory, he simply started a PPT in it.
　　 Last week, the elder sister considered that he had participated in the group meeting for the first time and had no experience, so she talked about his work for him. This week he will be playing by himself.
　　 First is the experimental progress this week, including repeatability testing and stability testing of device performance.
　　 Then he designed the synthetic route of the molecule.
　　 It seems that he designed four molecules, but they are actually four types of molecules, because there are so many changes in the synthesis.
"For example, you can change the size, type, position, and number of branches, you can choose whether to introduce heteroatoms, and you can change the position and number of heteroatoms.
　　 After he finished the group meeting PPT, all the simulation results came out.
　　 From the perspective of energy level structure and band gap, the four types of molecules are more suitable photovoltaic materials.
　　 However, it is only theoretical.