## Learn to Use ITensor

main / classes / customspin

# CustomSpin

The CustomSpin class is a specialization of SiteSet which initializes its sites to be of type CustomSpinSite, representing a spin with total spin quantum number S (= 1/2, 1, 3/2, 2, ...) where the user can specify S.

CustomSpin and CustomSpinSite are defined in the file "itensor/mps/sites/customspin.h"

## Synopsis

auto sh_sites = CustomSpin(100,{"S=",0.5}); //100 S=1/2 sites
auto S+_3 = op(sh_sites,"S+",3);          //obtain "S+" operator

auto s3h_sites = CustomSpin(100,{"2S=",3}); //100 S=3/2 sites
auto Sz_7 = op(s3h_sites,"Sz",7);          //obtain "Sz" operator


## Named Arguments Recognized

The CustomSpin class accepts the following named arguments. Only one of these needs to be provided:

• "S" — the total spin quantum number of the sites. For example passing the named argument {"S=",0.5} creates S=1/2 spins; passing the named argument {"S=",1.0} creates S=1 spins.

• "2S" — two times the total spin quantum number of the sites, which is always an integers. For example, passing {"2S=",1} creates S=1/2 spins; passing {"2S=",2} creates S=1 spins.

## Operators Provided by CustomSpinSite

• "Sz" — the z spin operator

• "S+" — the spin raising operator

• "S-" — the spin lowering operator

• "Sz2" — square of the z spin operator

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