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<div>Dear Minoru Otani,</div><div><br></div><div>I am trying to use ESM implemented in Q.E. and reading your code (esm.f90).</div><div>In ESM calculation, terms of “exp(x) * erfc(y)” often become overflow because of huge exp(x).<br></div><div>Thus, you prepare a special subroutine “exp_erfc(x, y)” to avoid the overflow.<br></div><div>Now, I have another idea to avoid the overflow, as following:</div><div><br></div><div>Operating an unit “exp(log( ))” to “exp(x) * erfc(y)”, one can obtain</div><div> exp(x) * erfc(y) = exp( x + log(erfc(y)) ) .</div><div>For boundary condition bc1, bc2, and bc3, it is easy to prove “x + log(erfc(y))” has </div><div>finite upper-bound. Thus, “exp( x + log(erfc(y)) )” does not become overflow.</div><div>Using “exp( x + log(erfc(y)) )” instead of “exp(x) * erfc(y)” in ESM calculation,</div><div>the overflow will be avoided. This method is accurate, not including numerical approximations.</div><div><br></div><div>Unfortunately, I have not ensured that this method is reliable for </div><div>exponential attenuated metal medium (bc4).</div><div>It would be great if my idea could help you to develop ESM code.</div><div><br></div><div>Regards,</div><div>Satomichi Nishihara</div><div><br></div>
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