polB_mpich: command not found

Have You tried accessing the binary with the full path?

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/polB_mpich - from package: openmx-mpich

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