Dear forum people The new position of the carbon atoms under uniaxial strain r in the framework of elastic theory is shown by the following equation: ri'=(I+ε).ri in which ri and ri' are the position of the carbon atoms before and after the strain is applied, respectively. I is the unit matrix and ε is the strain tensor which is attached. I can't calculate ri' . For example: δ1=a(√3/2,-1/2) δ2=a(0,1) δ3=a(-√3/2,-1/2) |δ1|=1+(3/4)ε11-(√3/2)ε12+(1/4)ε22 |δ2|=1+ε22 |δ3|=1+(3/4)ε11+(√3/2)ε12+(1/4)ε22 Can help me? How calculate |δ1|,|δ2|,|δ3|?