# 3.5. Example: Silver and Copper Clusters

Tip

The sample input and output files can be found in testfiles/atom/3-agcu.

## 3.5.1. Ag38 and Cu38

The systems here are two metallic clusters: $$\mathrm{Ag}_{38}$$ and $$\mathrm{Cu}_{38}$$. The interactions are modelled by Gupta potential. The parameters can be found in misc/atomic-force-field.txt:

misc/atomic-force-field.txt
Cu-Cu      0.0855         1.224        2.556      10.96        2.278     #  Phys. Rev. B 48, 22, 1993
Cu-Au      0.1539         1.5605       2.556      11.05        3.0475    #  Phys. Rev. B 48, 22, 1993
Cu-Ag      0.0980         1.2274       2.7224     10.700       2.8050    #  J. Chem. Phys. 2011, 135, 164109
Au-Au      0.2061         1.79         2.884      10.229       4.036     #  Phys. Rev. B 48, 22, 1993
Ni-Ni      0.038          1.07         2.491      16.999       1.189     #  Phys. Rev. B 48, 22, 1993
Rh-Rh      0.0629         1.66         2.69       18.45        1.867     #  Phys. Rev. B 1993, 48, 22
Ag-Ag      0.1028         1.178        2.88       10.928       3.139     #  Phys. Rev. B 1993, 48, 22
Ir-Ir      0.1156         2.289        2.72       16.98        2.691     #  Phys. Rev. B 1993, 48, 22


Attention

As mentioned in Theoretical Background, Gupta potential is not suitable for small metallic clusters. Here we just want to demonstrate the function of atom.

Consider $$\mathrm{Ag}_{38}$$ first.

Step 1: call abcinp to generate input files:

$abcinp Ag38 1 Gupta 10 100 100 5 20 38 Ag Parameters for atom-pair 0-0: A xi d p q > 0.1028 1.1780 2.8885 10.928 3.1390  Step 2: Run the global optimization: $ atom Ag38.inp > Ag38.out


After a few seconds, you will find the global minimum in Ag38.xyz (see below) and local minima in Ag38-LM.

For $$\mathrm{Cu}_{38}$$, the global optimization is similar.

Tip

You can try to search $$\mathrm{Zn}_{38}$$. Its global minimum has a completely different geometry from $$\mathrm{Ag}_{38}$$ and $$\mathrm{Cu}_{38}$$.

## 3.5.2. Ag32Cu6

Now we consider a mixed metallic clusters: $$\mathrm{Ag}_{32}\mathrm{Cu}_{6}$$. Will it have a similar global minimum with $$\mathrm{Ag}_{38}$$ and $$\mathrm{Cu}_{38}$$?

Step 1: call abcinp to generate input files:

$abcinp Ag32Cu6 2 Gupta 10 3000 100 5 20 32 Ag 6 Cu Parameters for atom-pair 0-0: A xi d p q > 0.1028 1.1780 2.8885 10.928 3.1390 Parameters for atom-pair 0-1: A xi d p q > 0.0980 1.2274 2.7224 10.700 2.8050 Parameters for atom-pair 1-1: A xi d p q > 0.0855 1.2240 2.5562 10.960 2.2780  Note that the population size 3000 and number of generations 100 are quite large, since this system is a difficult one for global optimization. Step 2: Run the global optimization: $ atom Ag32Cu6.inp > Ag32Cu6.out


After a few seconds, you will find the global minimum in Ag32Cu6.xyz (see below) and local minima in Ag32Cu6-LM. Unlike the face-centred-cubic truncated octahedron cluster of $$\mathrm{Ag}_{38}$$, this global minimum has somewhat unexpected D 6h symmetry.