OpticalConductivityMain_mpich: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/lib64/mpich/bin/OpticalConductivityMain_mpich - from package: openmx-mpich

You may install the required package with command yum install {package}

Error in other languages:
OpticalConductivityMain_mpich: bevel nie gevind nie
OpticalConductivityMain_mpich: comandă negăsită
OpticalConductivityMain_mpich: comando não encontrado
OpticalConductivityMain_mpich: commande introuvable
OpticalConductivityMain_mpich: command not found
OpticalConductivityMain_mpich: käsku ei ole
OpticalConductivityMain_mpich: không tìm thấy lệnh
OpticalConductivityMain_mpich: komanda nerasta
OpticalConductivityMain_mpich: Kommando nicht gefunden.
OpticalConductivityMain_mpich: kommandot finns inte
OpticalConductivityMain_mpich: komut yok
OpticalConductivityMain_mpich: nie znaleziono polecenia
OpticalConductivityMain_mpich: níor aimsíodh an t-ordú
OpticalConductivityMain_mpich: no se encontró la orden
OpticalConductivityMain_mpich: no s'ha trobat l'ordre
OpticalConductivityMain_mpich: opdracht niet gevonden
OpticalConductivityMain_mpich: parancs nem található
OpticalConductivityMain_mpich: perintah tidak ditemukan
OpticalConductivityMain_mpich: príkaz nenájdený
OpticalConductivityMain_mpich: příkaz nenalezen
OpticalConductivityMain_mpich: команда не найдена
OpticalConductivityMain_mpich: командата не е открита
OpticalConductivityMain_mpich: 命令找不到
OpticalConductivityMain_mpich: コマンドが見つかりません