在单三态能量差ΔEST以及磷光的计算中都会涉及第一激发三重态T1的几何结构优化。本文单独谈一下T1的结构优化。T1的结构优化常用以下两种方式：（1）将自旋多重度设为3，使用UDFT（非限制性DFT）来优化；（2）使用TD-DFT来优化，使用TD(triplet)关键词。以下我们通过两个例子来对比两种方法的优化结果。
一、联苯分子
优化基态的输入文件：
代码语言：javascript复制#p pbe1pbe/6-311G** opt
Title Card Required
0 1
C -2.09908937 0.62433012 0.00000000
C -0.69667737 0.62433012 0.00000000
C 0.00686463 1.82694412 0.00000000
C -0.67921737 3.04124012 -0.00276100
C -2.07387037 3.04933912 -0.00410600
C -2.78183137 1.84928112 -0.00129900
C -2.83952037 -0.63611388 0.00125500
C -2.40815137 -1.71412788 -0.78523500
C -3.11629937 -2.91403288 -0.78348600
C -4.25927837 -3.05309588 0.00359000
C -4.69372537 -1.98593688 0.78943600
C -3.99048837 -0.78310388 0.78885600
H -0.15162637 -0.33154288 0.00768300
H 1.10672063 1.81686712 0.00327200
H -0.12224837 3.98928512 -0.00385900
H -2.61816537 4.00512212 -0.00849600
H -3.88213737 1.86004112 -0.00794900
H -1.51013437 -1.60658188 -1.41200100
H -2.77215737 -3.75282488 -1.40621400
H -4.81617637 -4.00118288 0.00450100
H -5.59347037 -2.09282188 1.41300000
H -4.33345437 0.05459012 1.41453700
UDFT的输入文件：
代码语言：javascript复制#p pbe1pbe/6-311G** opt
Title Card Required
0 3
坐标略TD-DFT的输入文件：
代码语言：javascript复制#p pbe1pbe/6-311G** opt td(triplet)
Title Card Required
0 1
坐标略以下是优化得到的结构：
优化得到的基态结构中，两个苯环的夹角为39.9度，而TD-DFT和UDFT优化得到的夹角均为0度，两者一致。由于基态和激发态结构的差异，也使得联苯分子的光谱中能观察到较大的Stokes位移。
二、CPDT分子
结构如下图所示，来自文献Adv. Funct. Mater. 2020, 1910301，计算时将侧链简化为甲基。
UDFT的输入文件为
代码语言：javascript复制#p opt scrf=(solvent=chloroform) upbe1pbe/def2svp
[No Title]
0 3
C -4.27441500 -2.27361200 0.21562800
C -4.10289800 -0.95436000 0.10922600
C -2.79048500 -0.70090600 0.12183500
C -2.14232600 -1.86237600 0.22902900
C -3.01121800 -3.09411600 0.30036000
S -1.88629700 0.44048500 0.04446400
C -0.61228700 -0.31622600 0.12773500
C -0.82805200 -1.64431600 0.23486000
C -5.57527700 -2.56104800 0.19944200
C -6.26627400 -1.40498800 0.14989700
S -5.36607300 -0.23337600 -0.00310900
C 2.12610300 1.83386600 -0.03217000
C 2.77201200 0.67073300 0.06512100
C 4.08528200 0.91730200 0.03911000
C 4.26089600 2.23576700 -0.07562200
C 2.99868600 3.06120500 -0.13403100
S 5.34096700 0.17939700 0.10500000
C 6.23816000 1.34527700 -0.07352500
C 5.56378200 2.51127700 -0.11882400
C 0.81167800 1.61697000 -0.01821800
C 0.59615700 0.28877600 0.09084500
S 1.86967900 -0.46986400 0.16691000
C -11.61443982 -3.95076415 0.47232452
C -11.74659167 -5.25155927 0.78659067
C -10.67005589 -6.03358835 0.96782128
C -9.43913809 -5.51529723 0.83879395
C -9.33877111 -4.21464541 0.53173444
C -10.39108086 -3.40946319 0.34457975
C -8.19255853 -3.51959142 0.36820696
C -9.93097513 -2.18443152 0.00367941
O -7.07639588 -3.97938324 0.48541112
C -10.71255268 -1.18734349 -0.46568022
C 11.44754589 4.08455644 -0.72201735
C 11.51138846 5.38375359 -1.06290925
C 10.40002021 6.07974045 -1.35378676
C 9.20086856 5.47928980 -1.30274563
C 9.16555626 4.18624786 -0.95285511
C 10.25592151 3.46792143 -0.65635830
C 8.05932177 3.41897423 -0.83957488
C 9.86537643 2.19872795 -0.40735157
O 6.91948431 3.78555373 -1.02920097
C 10.70233435 1.14170220 -0.31668287
C 7.58408600 1.28441400 -0.05746600
C -7.60432000 -1.30125400 0.02166100
C 8.50757700 2.20642103 -0.40364757
C -8.57765221 -2.23207623 0.12233890
C -2.82666200 -4.01372800 -0.90841400
C -2.88360000 -3.82588100 1.63827600
C 2.84919900 3.98827900 1.07396800
C -12.02833839 -1.23426811 -0.56497771
N -13.18408882 -1.23188865 -0.66374030
C -10.25704015 -0.09407965 -1.04879248
N -9.88727401 0.86568539 -1.58492031
C 12.02001076 1.20810835 -0.33844275
N 13.17924977 1.23077795 -0.36457461
C 10.28528364 -0.10565884 -0.45628795
N 9.93893211 -1.19190004 -0.67409753
C 2.83540800 3.78478200 -1.47241500
H -0.08610600 -2.45000000 0.30979100
H -5.96666200 -3.58571600 0.20814200
H 5.98625000 3.52068900 -0.20939500
H 0.06936200 2.42246500 -0.09140100
H -12.53928772 -3.37659812 0.33764705
H -12.75453667 -5.68781782 0.89485477
H -10.79637682 -7.09915697 1.22255937
H -8.55153820 -6.15074752 0.98723032
H 12.39436279 3.57509994 -0.50283235
H 12.49196712 5.88784718 -1.11036999
H 10.47196716 7.14376164 -1.63494916
H 8.28530791 6.04433016 -1.53953759
H 7.96068829 0.27756903 0.20434873
H -7.94074014 -0.30174767 -0.31832409
H -1.81845500 -4.48644200 -0.89486400
H -3.58769600 -4.82673000 -0.90641300
H -2.92786100 -3.45445400 -1.86637900
H -1.88002500 -4.29827700 1.73660700
H -3.65199200 -4.62733600 1.72530800
H -3.01834300 -3.13122300 2.49850200
H 3.61331300 4.79793800 1.04752000
H 1.84289000 4.46507000 1.08426900
H 2.97335600 3.43398800 2.03213600
H 3.59848200 4.58824200 -1.58317600
H 2.95047200 3.08515500 -2.33156000
H 1.82835100 4.25409100 -1.54790400
TD-DFT的输入文件为
代码语言：javascript复制#p opt td=triplet scrf=(solvent=chloroform) pbe1pbe/def2svp
[No Title]
0 1
结构略两者优化得到的结构为
RMSD值为0.01 Å，差别非常小。两种方法优化都是37圈收敛，而UDFT使用的时间为3 h 30 min，TD-DFT所用时间为12 h 35 min，差别还是非常大的。计算在两颗Intel Platinum 8163 CPU（共48核）上完成。
从以上两例可以看出，UDFT和TD-DFT优化得到的结构基本是一致的，但是TD-DFT的优化时间要比UDFT长很多。一般计算中使用UDFT优化即可。
