写一个脚本，循环运行壳模型程序 bigstick.x，收集结果

BigStickPublick 可以从 github 上下载：https://github.com/cwjsdsu/BigstickPublick
在 BigStickPulick 路径下，准备好 usdb.sp 和 usdbpn.int (upn格式)，编写脚本跑遍 sd 壳所有偶偶核的能谱：

#!/bin/bash

# calculate spectrum and wavefunctions
# generate proper input file, and run bigstick

rm ../input/p*  # delete input files, as initialization

echo -n "Start running. "
echo $(date)
for(( pN=0; pN<=6; pN++ ))
do
        for(( nN=$pN; nN<=6; nN++ ))
        do
                Np=$(($pN*2))
                Nn=$(($nN*2))
                echo "Np=$Np, Nn=$Nn"
                filename="../input/p"$Np"n"$Nn"_cin_bigstick.txt"       # input file
                rm $filename
                touch $filename  # 准备一个 bigstick 的 std 输入文件
                echo "e">>$filename                                     # calculate spectrum
                echo "../output/p"$Np"n"$Nn>>$filename                  # output file name
                echo "usdbpn">>$filename                                # usdbpn.sp
                echo $Np"  "$Nn>>$filename                              # Np Nn values
                echo "0">>$filename                             # M=0
                echo "upn">>$filename                                   # format of interaction file
                echo "usdbpn">>$filename                                # interaction file
                echo "1 18 $(($Np+$Nn+16)) 0.3">>$filename              # scaling
                echo "1 1 1 1 1">>$filename                             # scaling
                echo "end">>$filename                                   # no more interactions
                echo "ld">>$filename                                    # lanczos default
                echo "5 2000">>$filename                                # keep 5 states, at most 2000 iterations
                time ./bigstick.x < $filename                           # run bigstick
        done
done

这个脚本自动生成一个 ../input/pxnx_cin_bigstick.txt 的输入文件，然后执行 time ./bigstick.x < $filename这一句，跑 bigstick 程序，输出能谱到 ../output/pxnx.res，文件中的内容是如下格式的：

  BIGSTICK Version 7.8.4 Apr  2018
  single-particle file = usdbpn
           4           4
           0 +
         120  iterations

  State      E        Ex         J       T
    1    -87.10445   0.00000    -0.000   0.000
    2    -85.60215   1.50230     2.000   0.000
    3    -82.98830   4.11615     2.000   0.000
    4    -82.73201   4.37243     4.000   0.000
    5    -82.03408   5.07037     3.000   0.000

下面的函数遍历 sd 壳偶偶核的 ../output/pxnx.res 文件，进行基态能量提取。因为壳模型相互作用具有同位旋对称性，所以只需要计算 (N >= Z) 的核，然后提取两个镜像对称核的（相同的）基态能量即可。

void GetSMEgs( double ** SMEgs ){
        double Egs;
        string reshead = "../p", restail=".res", res;
        for(int Np = 0; Np <=12; Np +=2 ){
                for(int Nn = Np; Nn <= 12; Nn +=2 ){
                        res = reshead;
                        if( Np < 10 ) res += (char)(48+Np);
                        else res = res + (char)(48 + Np/10) + (char)(48 + Np%10);
                        res += "n";
                        if( Nn < 10 ) res += (char)(48+Nn);
                        else res = res + (char)(48 + Nn/10) + (char)(48 + Nn%10);
                        res += restail;
                        cout<<"Np = "<<Np<<", Nn = "<<Nn<<", res = "<<res<<endl;

                        double Egs;
                        ifstream fin(res);
                        stringstream strm; string line, headword;
                        while( !fin.eof() && headword != "State" ){
                                getline(fin, line); strm.clear(); strm.str(line); strm>>headword;
                        }
                        getline(fin, line); strm.clear(); strm.str(line); strm>>headword >> Egs;
                        fin.close();

                        cout<<"Egs = "<<Egs<<endl;
                        SMEgs[ Np/2 ][ Nn/2 ] = Egs;
                        SMEgs[ Nn/2 ][ Np/2 ] = Egs;
                }
        }
}

这样就得到了壳模型 usdb sd 壳所有偶偶核基态能量，都储存在 SMEgs[ Np/2 ][ Nn/2 ] 里面。