public void  setSurfaceChargeDensity(double sigma){
        if(this.psi0set){
            System.out.println("You have already entered a surface potential");
            System.out.println("This class allows the calculation of a surface charge density for a given surface potential");
            System.out.println("or the calculation of a surface potential for a given surface charge density");
            System.out.println("The previously entered surface potential will now be ignored");
            this.psi0set = false;
        }

        this.surfaceChargeDensity = sigma;
        this.sigmaSet = true;
        if(this.surfaceAreaSet){
            this.surfaceCharge = sigma*this.surfaceArea;
            this.chargeSet = true;
        }
    }