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1、过渡态简单点说就是化学反应中瞬间形成的高自由能的不稳定复合物，形象点说就是就是反应势能面上的一个鞍点，所谓的找过渡态也就是要找到这个反应势能面上的这个鞍点，这里以DA反应作为例子简单说下我用gaussian找过渡态的经验。Gaussian里面找过渡态主要有3种方法：TS、QST2以及QST3。这里套用gaussian手册里的说明。TS是进行过渡态而不是局部最小值的优化计算。QST2是使用STQN 方法寻找过渡态结构。这个选项需要输入反应物和产物分子结构，先后通过两组连续的标题和分子说明部分定义。注意在这两个结构中的原子顺序必需一致。TS 不能和QST2 合用。QST3是使用STQN 方法寻找过
2、渡态结构。这个选项需要输入反应物，产物和最初的过渡态结构，先后由三组连续的标题和分子说明部分定义。注意在这三个结构中的原子顺序必需一致。TS 不能和QST3 合用。接下来贴出几个例子来说明下TS、QST2和QST3的输入文件该怎么写%chk=c2h4_c4h6_ts%nproc=1%mem=200mb# opt=(ts,calcfc) freq=noraman b3lyp/6-31g*Title Card Required0 1C -0.37960200 1.41026100 0.50972400H -0.06409400 1.04025400 1.48028400H -0.26589500
3、2.48067200 0.40089100C -1.26020300 0.70558300 -0.28508700H -1.84635800 1.22289600 -1.04415700C -1.26023800 -0.70552500 -0.28508700H -1.84641800 -1.22280900 -1.04415900C -0.37967300 -1.41024700 0.50972300H -0.06414500 -1.04025600 1.48028200H -0.26601500 -2.48066300 0.40088700C 1.45648200 0.69084700 -
4、0.25401700H 1.98402400 1.24692000 0.51079100H 1.29283800 1.24312300 -1.17152100C 1.45645300 -0.69091000 -0.25401800H 1.29278400 -1.24317800 -1.17152200H 1.98396500 -1.24700700 0.51079200qst2%chk=c2h4_c4h6_qst2%nproc=1%mem=200mb# opt=(calcfc,qst2) freq=noraman b3lyp/6-31g*Title Card Required0 1C -3.1
5、7791906 1.13289796 -1.01187682H -2.64475531 0.20519304 -1.01187682H -4.24791906 1.13289796 -1.01187682C -2.50264475 2.30787525 -1.01187682H -3.03580850 3.23558018 -1.01187682C -0.96264475 2.30787525 -1.01187682H -0.42948100 3.23558018 -1.01187682C -0.28040135 1.13693077 -1.01187682H -0.80804382 0.20
6、607449 -1.01187682H 0.78957977 1.14328807 -1.01187682C -2.59776413 0.98894279 1.10133233H -3.14031063 0.06692559 1.12200992H -3.12699887 1.91846375 1.07302387C -1.24260873 0.98347968 1.11087410H -0.70006223 1.90549689 1.09019651H -0.71337398 0.05395873 1.13918256Title Card Required0 1C 1.41432400 0.
7、09460100 0.31826800H 1.42370000 0.10775400 1.42899000H 2.47445600 0.12780100 0.00402400C 0.66866000 1.30146700 -0.16992700H 1.26438900 2.14276400 -0.50621500C -0.66890700 1.30134300 -0.16992700H -1.26479300 2.14252900 -0.50621700C -1.41434600 0.09433800 0.31826600H -1.42372700 0.10749400 1.42898900H
8、 -2.47448400 0.12734000 0.00402000C 0.77040400 -1.21422100 -0.17552700H 1.14229400 -2.05288100 0.44176200H 1.12544800 -1.41421500 -1.20543600C -0.77017000 -1.21437000 -0.17552800H -1.12517200 -1.41443600 -1.20543700H -1.14189800 -2.05310200 0.44176200qst3%chk=c2h4_c4h6_qst3%nproc=1%mem=200mb# opt=(c
9、alcall,qst3,noeigentest) freq=noraman b3lyp/6-31g*Title Card Required0 1C -3.17791906 1.13289796 -1.01187682H -2.64475531 0.20519304 -1.01187682H -4.24791906 1.13289796 -1.01187682C -2.50264475 2.30787525 -1.01187682H -3.03580850 3.23558018 -1.01187682C -0.96264475 2.30787525 -1.01187682H -0.4294810
10、0 3.23558018 -1.01187682C -0.28040135 1.13693077 -1.01187682H -0.80804382 0.20607449 -1.01187682H 0.78957977 1.14328807 -1.01187682C -2.59776413 0.98894279 1.10133233H -3.14031063 0.06692559 1.12200992H -3.12699887 1.91846375 1.07302387C -1.24260873 0.98347968 1.11087410H -0.70006223 1.90549689 1.09019651H -0.71337398 0.05395873 1.13918256Title Card Required0 1C 1.41432400 0.09460100 0.31826800H 1.42370000 0.10775400 1.42899000H 2.47445600 0.12780100 0.00402400C 0.66866000 1.30146700 -0.16992700H 1.26438900 2.14276400 -0.50621500C -0.66890700 1.30134300 -0.16992700H -1.2647930
