esp_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/esp_mpich - from package: openmx-mpich

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

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