• Use Spartan or WebMO to optimize the structure of the following molecule with B3LYP  theory with 6-31+G(d).

Notice that different multiplicity might cause different structures, compare the energies of the structures too.

1. Make an initial structure of the compound with Spartan, then save the file as .mol2 format.
2. Using the input file with the optimization command ,multiplicity is singlet & triplet . 
3. Run the input file with Gaussian . 

energy(hartree):      -2941.330941                                                                         -2941.322697

Conclusion: The tetrahedral structure has lower energy , so this structure tends to be the tetrahedral one.

• Plot the eletron density of He and He- and use MP2 theory with d-aug-cc-pVTZ and aug-cc-pVTZ  basis sets.

1. Take He(aug-cc-pVTZ)for example.  Create a " He-aug.com" file.   
2. Calculate "He-aug.com" file, then getting "He-aug.chk" file.
3. Enter "formchk" (command) for getting  "He-aug.fchk" file.
4. Create a "xyz.dat" file and use cubegen to get a "He-aug.cube" file.

xyz.dat:決定生成的範圍以及掃描的平面

第一行第一個數字 -1是要讀取這個文字檔，後面 3 點為起始做標(這次使用0.0 0.0 0.0為起始)

2.3.4行 分別為 x、y、z

第一個數字是 number of points，(-) 表示單位Bohr，(+)表示單位Angstrom。(這次使用Bohr)

每 (x, y, z) 向量單位 掃描一次 

(Ex：在x方向取 800 個點，x 軸方向每 0.01Bohr掃描一次)

5. Gain data from "He-aug.cube" files and make graphs.

Result

This plot show that adding diffuse functions could make caculation better.