awk 'NR==FNR {   # Read the first file (./tmp_mmzero_5-15)

    hash[$1] = $1  # Store the first column as the key in an associative array

    next

}

NR!=FNR && $1 in hash {    # Check if the first column of the second file is present in the array

    print $1, $2   # Output the first column of file_1 and the second column of file_2

}' ./tmp_mmzero_5-15 E_QM-MM_zero.dat

​

​